Jim, the Adcom power amp certainly won't adversely affect the sound quality. But you already have a flagship receiver with a darn good power amp section, too. Judging from my own experience with my Pioneer 45TX receiver (rated 110W/ch @ 8ohms) and my Adcom GFA-555II power amp (200Wx2 @ 8ohms), you will be hard pressed to hear a sonic benefit of the Adcom amp, especially given the very high sensitivity/efficiency of the M80s. I myself cannot hear a convincing difference between the Pioneer receiver's own power amp and the Adcom -- with my Hales front speakers (
mere 89dB/W/m efficiency) in over 5000 cu. ft. room.
If you still want to add the Adcom, I would definitely go with a pre-owned item that you can find at AudiogoN.com and other places. You will save tons of $$$ without losing anything (well, perhaps a couple of scratches on the case top) -- the Adcom amps are so super-reliable, you have nothing to worry about buying pre-owned.
Anyway, congratulations and welcome to the Axiomville!!!