Disclaimer: I am not a professional reviewer. My train of though is cumbersome and I am usually wrong.
Just to give you an idea, my chain is a Note 4 HDMI out > HDMI to Optical converter > PXA-H800 > NVX JAD 900.5 > IA C6 and Alpine SWR-T12 x 2
After the normal tuning and break in period I came to a few conclusions on this set. For starters they are not very hard to drive with my not so powerful amplifier, they can get very loud, to the point of drowning a mustang with a loud-ish muffler. These can be driven pretty hard with not much power. The tweeters are very picky when it comes to installation location. I tried a few places with the worst being mounted behind the factory location inside the A pillar to keep a factory look. Strangely enough (not strange at all), the best location was mounted off axis on the A pillar. what this did was to move them forward an inch or so and they became alive.
These tweeters have a good balance between in your face and laid back, they sit somewhere in the middle. They are extremely pleasant to listen to and give very little listener fatigue which is a huge plus. Sometimes I find myself tuning out the sibilance, but it was not the case with these. They are smooth but I wouldn't say they are warm. As a matter of fact I think they lean a little towards being bright, but again, they are not tiring to listen to at all. I have other tweeters I can use as references to compare these. The Dayton pods (ribbon) are very nice, but can get tiring to listen to, these don't. The top of the line Image Dynamics (XS?) are very beautiful tweeters and pleasant to listen to but those I think are on the warmer side, not as bright as these but not much difference. The one that would get the closest to the C6 tweeter withing my experience would be the HAT L1.
I found very difficult to tune the Dayton Pods, I tried my best to get rid of the listening fatigue, and I got close but it was always there. Could not crank them for long. I found them hard to tune, maybe I was asking too much of them.
The image dynamics was a lot easier to tune, after a few passes I got them to where I was happy. The C6 and the L1 required very little of me to tune. They pretty much sounded really nice to begin with. Some speakers are like that, and even though this is entirely subjective to my taste I found these two very easy to live with. Are these C6's nice tweeters? Hell yes! Would I recommend them? Hell yes! Would I buy them again? You know the answer. The icing on the cake is that sexy copper dome, gorgeous.
On to the mids. These are beautiful speakers, they seem very well made. The story here is a little different. Setting my crossovers per the IA website I found that the mids were bottoming out on some songs, badly. I tweaked and I tweaked and I finally got them to where they very rarely bottom out. I now have them crossed over at 90Hz with a 24db slope and they sound very good. For my taste I wished they played a little lower with more ease. Don't get me wrong, these sound very nice but they don't have the kick the Image Dynamics (XS) had. I had those crossed over at 63Hz and they were phenomenal. Again, these are not hard to drive and don't require too much power to be driven hard.
As a whole I had to allow a little of the higher frequencies at a lower volume from my subs to compensate a little, it works. The set imaging is outstanding, but I think that has to do a lot with the tuning. Weirdly the PITA Dayton PODs imaged with pinpoint accuracy, all others imaged really well. The transition in frequencies between tweeters and mids is very well executed, there is some wiggle room to play. The Dayton's crossover point is way high and I think that tweeter is more well suited for a three way set, but you can make it work in a two way set, just no wiggle room.
Price? They are expensive. Are they worth it? They are better than the XS is some ways, but not in others. You need to determine if they are worth it yourself. I LOVE this C6 set, but knowing what I know now I would have gone with the C6 tweeter and the XS mids. Or for half the price you can get the XS set and call it a day. For the more discerning listeners the C6 will be the way to go.
Songs listened to:
Andy Summers - Charming Snakes: This speakers made me rediscover how beautifully recorded this album is. The sound is just so 'clean'. The bass notes are very well defined and C6 (along with the subs) executed them beautifully. The cymbals are almost as if they were there, next to you. The snare's presence is unreal, this is one of the few albums where the snare can make me blink if played loud (the C6 can do that with that little amp). This is a must album to test your system and the C6 passed with flying colors.
Dire Straits - Lover Over Gold: Another beautiful recording. The piano in Love Over Gold is very sweet sounding. The synthesizers fill up the space in a way I have not heard before. Mark Knopfler's voice is centered and well defined. You can hear the nuances I knew were there.
Alanis Morissette - Little Jagged Pill: Her voice is amazingly clear, I had never realized how well recorded this album is.
Minus The Bear - Minus The Bear: This is one of those cases when an album that is not so well recorded sounds really good.
U2 - The Joshua Three: This is one of the cases when an album that is not so well recorded sounds like complete and total shit.
Die Antwoord - Donker Mag: I didn't expect much of this album but I was pleasantly surprised. A bit bassy but a very clean and balanced otherwise.
In a scale from 1 to 10, 10 being the best:
Overall Sound - 9
Tweeter - 10
Mid - 8
Build Quality - 10
Value - 6
Packaging - 10