I was running the M60s stereo with an HK 3270 and am now running them in 5.1 (7.1 if I ever wire up the back M2s) with an HK 630.

I'm not a big believer in noticeable sound differences between comparably high end receivers, so I will just describe the sound as "solid" and "smooth"

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