Passively biamping with amplifiers having very different power capabilities creates an additional problem, besides the need to gain match and the possibility of sonic issues due to the amp's having differing sonic characters. You would not be able to utilize most of the power capability of the higher powered amp.
Your Classe amp is rated at 800 watts into the 4 ohm nominal impedance of your speakers. The BAT is rated at 60 watts into 4 ohms. In a properly gain matched passive biamp arrangement both amplifiers have to output identical voltages at any instant of time, in a given channel, corresponding to the full frequency range signal. Therefore you would not be able to raise the volume control high enough to utilize most of the power capability of the Classe amp without clipping the BAT amp, which if clipped would result in severe distortion and possibly even blown tweeters. In effect, you would be converting the 800 watt Classe into perhaps (just guessing) a 100 or 150 watt amp, depending on how much voltage the BAT amp is capable of putting out.
Using an active crossover ahead of the amps would resolve that problem, at least mostly, and would also presumably allow you to gain match. You would still be left with the possibility that sonics may be adversely affected by the different sonic characters of the two amps, particularly at frequencies that are in the crossover region, where both amps would be contributing to the sound that is heard.
I have no particular familiarity with active crossovers, but if you want to go that way models that should be looked into are made by Marchand, Bryston, and Rane.
Regards,
-- Al
