What about just getting a good stereo power amp for the mains and letting the receiver handle the rest ? It just seems like you need some really hefty thermal management to power lots of channels at 4 ohms in one amp. Not impossible but probably expensive...

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8