No, I don't think you'd need crossovers if you're going active, which implies using a crossover that handles those functions for you. It's hard to find an amp that doesn't have something on board though- either a high-pass or low-pass function of some type. They are out there though, but I can't think of any off the top of my head.
All amps have some sort of gain though.
Look for something with a known good reputation, lots of people here have bought and sold stuff with little or no problem, so you might find some good deals in the classified section. As long as it fits (trunk/boot under a seat or wherever) and you can supply it with good power and grounds, along with adequate sized speaker wire... the world is your oyster.
Me personally, I'd try to buy as much power as possible; say 125 x 4, but there are many amps out there with smaller power ratings that simply drive a good set of speakers with clarity, dynamics and plenty of headroom.
First off Budget: If I were to buy "new" as in buying online from sonicelectronix.com or woofersetc.com I would spend 200-300.
If I were to buy on the classifields section on this forum I would spend anywhere from 150-225
Same thing with craigslist.
I need a 4 channel.
Space is an issue. This will be mounted in rear corner in trunk in my 05' LGT, I will have to get dimensions but I believe I have 14" by 14" to work with so i am going to need a small amplifier. Amplifier Will be place in (fiberglass enclosure) upside down so "guts" are showing for display behind either glass or plexiglass, so I wouldn't mind buying a use amplifier cuz I could care less about scratches or dings.
I need something with fairly good crossover settings correct?
Now that the wider the range, the better the amplifier?
If you are looking at the PPI Arts I would PM PPI Art Collector. I was looking at those amps last week and after PMing him it made me realize that it might cost more money to go old school and have them pugraded to be up to par. He has some good advice... or I can copy and paste his PM to me and send it to ya.
I have always been a fan of the Memphis amps but like you mentioned... they are not always size friendly. Keep in mind the PDX lol. If you are really interested in one let me know. I will work with ya on it. I have an extra 4.150 and 600.1 if you want a matching sub amp.
When I made the choice to go active I looked at power, size, and THD. I think I mentioned it to ya before... but having this much overhead is great. 150x4 rms and litteraly not having to turn up the gains at all.
A havent noticed a huge advantage yet going active but have a new comp set coming in next week so I will be able to make alot more adjustments. The mids that are coming can hold alot more then the tweeters, so I will enjoy it then.
I think part of it depends on whether or not you're going to use a processor. With the MS8, all I need is a gain setting, all of the other features are useless. If not, you might want to look into what crossover features are available.
I also look at power, size, and THD. I love small class D amps. I have one JL HD600/4 under the passenger seat and getting ready to add a 900/5 under the driver's seat. Having only two amps that fit under the seats to power an entire 3-way active front with center and subs is awesome. Power and headroom is great.
The h660 will gives you a high pass in the front, a bandpass in the front, a high pass for the rear and a low pass for your subs. As for amps, look for the power you need and you will be fine. jl300/4 or a 450/4 will work well.