You only really get a benefit from two amps if you have an electronic crossover before the amps that just sends low notes to one amp and high notes to the other amp. Without an electronic crossover you're still amplifying all the signals in both amps so you're not really gaining anything.
Then again I always thought the best thing about bi-amping was being able to crank the volume until the amp driving the woofers was clipping like crazy and still have clean sound coming out of the mids and tweets
IIRC the lower set of terminals on the M80 goes to the woofers through the woofer part of the crossover, and the upper set goes to the mids and tweets through the mid/tweed parts of the crossover.
