Got the amp rack layout sorted out. Won't have to stack after all. Just had to get a bit creative, and ended up staggering the amps a bit, since only the FD4150 is the longest and the USB 4085 is the shortest.
Right now, the side supports are 3.5" high. I need to trim them about half an inch, to reducte the overall height as such, while making sure that the amps have enough clearance and the 80mm fans can fit in the back. 3" will be perfect. All amp controls are at the front (where the removable front panel will be), so tuning/adjusting should never be a problem.
Here's the "planned" system [COLOR=blue !important][COLOR=blue !important]diagram[/COLOR][/COLOR], now with the 3Sixty incorporated.
Most everything is straight forward except for that damn rear fill signal. I'm thinking just a L-R signal, MONO, time delayed, attenuated and bandpassed, but fed to both rear fill sets should still be ok? As opposed to a stereo rear fill signal (as in L-R, and R-L), and if that's the case, can I just switch the phase of the right/left signal to make em stereo?