How about a stereo receiver?
If I understand you use correctly; occasional set-up for a party and then returning the speakers back to the HT until the next big bash.
I would give a hard look at a capable stereo receiver instead of a HT AVR, so the money spent is in the amps driving the M80s vice the other 3-5 channels.
For example either the HK 3390 (80W/ch) or 3490 (120W/ch), or the equivalent entries from Yammy, such as RX-797 (100W/ch).
For occassional party use, I would also try to find one used if I could.
Cheers,
XEagleDriver