Just my .02 cents, but I have found that 2 identical amplifiers are the only way to accomplish this successfully. There are very few exceptions. The two most important things in my opinion are rise time and input sensitivity. It is possible to compensate for differences in input sens. by attenuating one of the amplifiers, but rise times (and input impedances) are a whole different animal. A crude analogy would be using a seperate car engine to drive each axle. One engine is a four cylinder engine, the other the same engine but with a turbo. The engine speed will not rise and fall at the same speed, creating an anomoly. The human ear is extremely sensitive to the timing of sound - having identical amplifiers delivers a coherent signal. I have heard systems where people used tubes on tweeters and solid state on woofers, and in my opinion it fails to be cohesive. One of the few exceptions to this would be to use a McCormack dna .5 deluxe on the top end, and a standard dna .5 on the bottom, as these amplifiers have identical input specs. I may be overtly picky about this, and if you were really interested in trying the bi-amp contact B&K and get the specs for input sens. and input impedance. If they match, go for it.
