Unless you are using an active cross-over with gain control, stay with the same amp. Otherwise, you will have all sorts of matching difficulties. You can put each B&K very close to each speaker (one amp per speaker) and run very short cables. I would prefer that set-up to a multi-channel. M/Ls are very revealing and difficult loads to drive. They benefit more from short speaker cable runs than most speakers.
Bi-amping advice for M/L Aerius
I am interested in bi-amping my M/L Aerius. They presently are running off a B&K Ref 2220. Would my best be to get another 2220; or could anyone recommend another amp that would match it well?