Gain matching of power amps

Gain is gain, it is constant no matter what the input voltage (until clipping, that is). So yes, in theory your hookup would work. The only caution has to do with tolerances, i.e., is the gain exactly 29.0 dB or is it actually 28.2 dB? Same goes for the other amp. You would need a high quality calibrated voltmeter to be certain.

Edesilva, you are correct. Gain in dB is additive so your math is correct. You are also correct about amplifiers being nonlinear. However, a well designed amplifier will keep this non linearity to a small fraction of a dB and shouldn't be of concern.

Miketw and Edesilva: Neither of you mention whether you have considered using an active crossover, which I consider the best way to do biamping. The individual speaker drivers should not really be receiving the full frequency range from the respective amps driving them. The overall goal of biamping is to split up the signal after the source/preamp and send a limited range of frequencies to the appropriate amp and then driver.... bass signal (say <200Hz) to the bass amp and then directly to the woofer, etc. Another advantage of the active xover unit is that most allow volume adjustments, so that the signal level going to each amp can be can equalized. This helps some with the gain issue, but as Herman has nicely outlined, you still don't want amps of wildly different gain involved. By the way, I'm not convinced that it always works to have SS for bass and tubes for mid/highs, since some speakers reveal the sonic differences between such amps at the crossover point. Some experimentation is obviously required for each case.

Thanks for the info, I'm still thinking about what to do when I move in 1.5 mo. and can unpack some gear in boxes, and its food for thought. Martin Logan actually recommends bi-amping my Prodigys with tubes up top and SS below. I was going to use a pair of ARC VT100s I have, but now am thinking of watching for an old ARC D400 and using the extra VT100 elsewhere.

In my case, Ral, the Casablanca can be turned into an active x-over. All things being equal, however, I'm not inclined to go active b/c I'm not sure I can replicate the job the ML x-overs are doing and the marginal volume doesn't really mean that much to me.

I always thought the "purists" suggested avoiding an active x-over anyway to eliminate "yet another thing in the signal path"... (Obviously, doesn't apply in my case, 'cos the Casablanca is there anyway).

Edesilva: I didn't know that about the Casablanca... interesting. I see your point about not trying to recreate the ML crossover. And yes I think many purists want to avoid any signal processing between source and amp, and this is quite reasonable. However, in a few cases a good active xover can actually improve things if the speaker's passive xover system is not so great (that was my case with the Maggie 3.6R factory bass-to-mid xover box). A Marchand xover (deluxe version with upgraded parts) has worked well for me and introduces negligible sonic signature given the overall improvement from biamping. I've read that the Bryston xover is pretty neutral too. Probably there are other good ones.