now i have not gone through the full thread but i had to say something. EVERY amp has its own sound. true its hard to find a way to A-B each brand to find one you like but a good audio shop will make sure their demo board is set up properly and even though they are in a different enviorment but any good ear or anyone who knows what to listen to (taking about SQ and not SPL so the person needs to know what TRUE good SQ sounds like). at all the shops i have worked at, managed, or just built the display boards i have always been able to hear a difference in quality of amps. now it does also matter what kind of speakers are being playing along with the type of head unit and the quality of the install parts. everything in the system plays major rolls in who things sound. some head units cause amps to sound warmer because of the quality of the inputs. example did an install with a Sony (customer had to have it) and at the shop i worked at install all XTANT amps (the removable cover ones where the chip sets were needed to adjust them) along with ADS 336is (the install was awhile ago) and the XTANT hex 12 subs with a cut through on f-150 Harley truck. after spending hours trying to tune the truck to sound good (because we knew what the amps and speakers were capable of sounding like) but no matter what we did it was bright as hell and mid bass sucked and the subs were super punchy (more then they should have been). so just to test we swapped out the deck to a clarion dxz835MP (with dual 24 bit dac also one of my favorite decks still using one today, the sony said it was 24 bit dacs and high voltage pre out) but as soon as we put in the clarion the system can alive and sounded so bitchen, warm, clear, crisp, subs sounded great, it was a night a day difference. needless to say customer kept the clarion. now in my personal car i have REALM amps (SCOSCHE/efx high end amp line well was) witch i have a 150x2 and 1100 or 1200 mono. all hooked to a clarion 835 and old school Memphis msq6 (old high end comp set with orange baskets still one of my fav speakers ever) and everyone who sits in my car goes wow sounds great how many speakers and how many mid bass do i have. when i show them what i have just two 6 1/2 comps with silk tweets and one 12 in a vented box, they are always shocked. its super warm mid bass for days only thing is to some people the highs are not bright enough witch i hate bright tweets that go tstststststs. well i swapped out my 150x2 true AB amp and install the MMATS HiFi-6150D (bitchen amp 150x6) but only using the front two channels, the warmth was gone and mid bass went down and over all i was very unimpressed. ended up taking it out. even the sq4100 has a warmer sq sound the the 6 channel. (still have yet to hear a awesome sq system with class d amps not saying its not there but i have not heard it) but that was in my system in my car. what im trying to say is all amps sound different (ab, tube, and D) and anyone with a decent ear will be able to hear a difference if they have a good way to a-b test the amps. plus it all depends on what other gear is in the car like head unit (also if using CD, ipod, ipod format quality, mp3, or the best dvd audio), speakers, the quality of install accessories and most importantly the system needs to be install CORRECTLY and tuned correctly. just think about it this way someone can have a car with the biggest badass motor, with a fully built rear end and nice wheels. but if all the connecting parts are junk (aka install accessories rca's power wire etc), suspension in stock and stock tires the car will go fast then before but not anywhere as fast as it could go if the connecting parts were matched (match but doesnt mean same brand im not a fan of a full same brand system). plus different head units playing different sources will also make amps sound different also depends on the speakers. but most importantly the install needs to be done correctly. i have heard some car that i was impressed on the sq when they were using low to mid end equipment and also been very disappointed in sq on some cars that were full hi end but crappy install. now if adding a processor in the mix that can change things majorly. plus im sure (i have not played with too many processors so cant truly say) each processor will produce different quality of sound. cheap experiment to prove my point would be if there were components try to swap out just the cross overs. then see how they sounds. maybe it will surprise you. same goes with amps. even if its the same power out put and same speakers but each amp is built with different power supplys, different caps, different preamps, etc, witch all leads to different types of sound going to the speakers (i say different type of sound because it may not be a bad thing or even a good thing just different type of sound). also just swap out head unit theres another test that can be done. i can tell a big difference between my clarion 835mp, alpine cda9815, eclipse 8053, eclipse 8443, old alpines like the true SQ old school, pioneer (old upper end one not sure the model but it wasnt cheap), and many other decks i tried. they all had their own sound some were good sounding some where just bla and flat and i always go back to the trusty 835mp. but again that is what i have found best for my set up with my car and i have about 500lbs of sound deadening witch also makes a huge difference. so again goes to install quality along with matching the right components (i dont mean matching brand i never heard and yet to hear a full brand matching system sound amazing) just match the right quality stuff together. also any REAL high end shops will work with anyone who is truly serious about getting a new amp that if the customer is not happy with the sq they should (well the store i managed) would try a few other amps until it has the sound the customer likes. PLUS ONE MAJOR THING IS everyone is different and will hear things differently, so one person may love it one may hate it. its all preference but if anyone is saying all amps or even all amps that are in the same quality class sound the same truly do not know what they are talking about and must not have any real experience with different set ups. i was luck enough to be in car audio for over 12 years and about 6 of them was installing and managing shops so i was able to try out different amps, speakers, head units, wires, etc and i learned what i wanted for my own system that way i got the sound i was looking for. tube amps sound extremely warm (but sometimes they lack the highs also on tube amp i learned that its better to get the biggest (most power output) you can so the amp does work as hard, since they can tend to loose their sq when all the way cranked (depending on the brand that is), also class d amps are great for subs and small space setups but i have yet to hear a true sq system YET not saying its not there but with out using any processor other then whats in the deck i would bet money any day that a true class AB amp with sound richer warmer and better then any class d if the person wants TRUE SQ and that person knows what TRUE SQ sounds like(i have talked to many people who think they know SQ until they here a TRUE SQ car and they its funny to watch them rethink everything they thought they knew. now the bet on class ab vs class D amps on mids and highs for SQ will stand until im proven wrong (witch someday will happen HOPEFULLY but until that day i will keep saying that AB amps will out perform class d amps and class D is for subs only). also just think about this your system is only as good and the weakest link in the chain. so make sure if you really want SQ take your time matching products up and also make sure you use good quality install parts. it will be worth it in the end even if you have to slowly build your system it will be worth it. now there are some cases where some things like high end RCA's where it wont be a noticeable difference like monster RCAs are a joke and they sound the same as other high end cables for half the cost. but like i said any REAL TRUE HONEST UPPER to high end shop should be there and help you decide and will be honest if the $ is worth it (well thats how i used to do things i made sure to never sell so called snake oil products to people who true cared and only did that when either the person was a prick, it was a show car (sponsored), or thats just what the person wanted but i still tried to match it with the rest of their system. its a shame that a lot of shops out there just want to sell things and make a quick buck and dont give a crap about audio. a good audio shop will have employees who are truly into car audio as a passion (eat, sleep, breath it) and there will be atleast a couple cars with full system in them or at least person project cars being done. any shop that does not have any owner or employees car loaded up with a good system is a shop i would be VERY care full at and i would double check everything they talk about because if they never use the products on their own and have a passion for audio, then most of the time the shop is just in it for the money. also any good shop will make sure their customers are happy (even though once in awhile some people are NEVER happy no matter what) but over all a good shop will do everything they can to make sure the customer is happy with their purchase even if it means swapping out amps or whatever to make it happen or tell you what you need to make it sound awesome (some cars need a processor or a single summing product to get best sound (like adding bass in a benz cl550 witch has the bose system where the the louder the system is the bass flattens out and falls out when it shouldnt be and some people are ok with that but true sq people will not be). sorry for long post just hate it when people talk about stuff that they truly have no clue what they are saying and their only real experience they have is with low end or Walmart equipment. its one thing if your on a budget and get only what you can afford and its another when they become MR. or MRS. know it all just because they installed their own or a buddies system and its the first or second car they have ever heard. plus things change and everyone is different. but over all each component plays their part in the system and they all create different sounds and again a system is only as good as the weakest link (ie: using low end power wire like CCA (unless the correct guage is used witch will end up costing near 100% copper wire would cost) like a garden hose if there is a kink in the hose or if the hose is too small the water flows less, crappy power wire starves amps even if they still work and sound ok but its not giving the amp what it truly needs.
thanks
tim