The potential issue with using different amplifiers in a biamplified system is not due to different gain levels or sensitivities. It is (again potentially) due to different propagation times for the different amps. In other words, how long an amplifier takes to process the signal from the input terminals to the output terminals.
I'm driving VonSchweikert VR100XS system using a pair of Lampizator True Balanced 211 Monoblock amps to on the midrange/tweeters and a pair of Spectron Musician III Mk2 monoblocks driving the woofers. The XS subwoofers get their signal from sense cables attached to the woofer inputs, integrating the bass input signal and the backwave EMF from the tower's woofers.
I've used other combinations of amps on the top and bottom of various speakers and in every case the combined strengths of the different technologies were far superior than biwiring with a single amp. In my system, the 211's bring excellent time coherence, detail, and timbre resolution. The Spectrons provide essentially limitless power (I've never heard them sound stressed), very high damping factor, and extremely extended bass response. As the saying goes, horses for courses.