I had a pair of M800's (upgraded to Signature 800's). I initially used a Threshold S450E which was fine. I then tried a Goldmund 9.5++ and a Goldmund 29, each of which sounded great, but neither of which was reliable. I then finally upgraded to Levinson 33H's, which were (and are) out of this world (be sure you have a dedicated 20 amp circuit for each one, though). I tried the Bryston 7B's, and they left me cold.
If you don't have one, I strongly recommend that you try to find an old Krell bass alignment filter for use with the M800's. The standard one from B&W is not very good, and if you don't use any bass alignment filter, you won't hear what the M800's can do in the bass region. With the Krell, they are truly awesome.
If you don't have one, I strongly recommend that you try to find an old Krell bass alignment filter for use with the M800's. The standard one from B&W is not very good, and if you don't use any bass alignment filter, you won't hear what the M800's can do in the bass region. With the Krell, they are truly awesome.