I've had Quarts for years and love them.
I just installed QSD-216 in the front doors (6.5" comps) and DKE-168 (6x8 coax) in the rear. A minute amount of trimming of the metal on the door with a Dremel was all it took for the front. The stockers fit like nothing was ever done.
They can be quite bright for many people, but I set my crossovers to -3 and they sound awesome. No way can I overpower them.
The system is the best I've ever heard, and I'm still not finished tweeking it
No experience with the subs.