Yes, I am still running a single Xtant X604 amp (75w x 4) for my entire SQ setup. Also I do not have mid-basses, just a simple 3-way setup of tweeter, midrange, subwoofer.
Here is the breakdown of which channel is doing what:
Channel 1: left front, 80Hz and up (using x-over in amp @24db/oct). Connected to a 5.25" mid in the kick that rolls off naturally on the high side plus also to a tweeter (in the center of the 5.25" mid) with a dedicated HPF 18db/oct @ 3.5k.
Channel 2: right front, 80Hz and up (using x-over in amp @24db/oct). Connected to a 5.25" mid in the kick that rolls off naturally on the high side plus also to a tweeter (in the center of the 5.25" mid) with a dedicated HPF 18db/oct @ 3.5k.
Channel 3: left sub, 80Hz and down (using x-over in amp @24db/oct). Connected to an 8" sub mounted in the front door in place of the factory location (with modification) and using the factory grille in the door.
Channel 4: right sub, 80Hz and down (using x-over in amp @24db/oct). Connected to an 8" sub mounted in the front door in place of the factory location (with modification) and using the factory grille in the door.
The 12" subs that can be seen behind the backseat or from the trunk were NEVER on unless I was doing an spl run for about 5 seconds at a competition. And if the 12's were on, the rest of the system was off. In fact, the 12's are not in the car now at all and have not been used since sometime in late 2005.