I agree 100% this can be tricky to pull off. I have done this several times on other speakers (Vandersteen mainly, Thiels once, Merlins briefly) that had bi-wire type of inputs (ahead of passive crossovers). There are many other threads addressing the merits of vertical vs. horizontal biamping and whether it's worth it at all. There also some inherent risks of making costly mistakes, so you have to watch what you're doing.
In ALL cases I have used two of the same stereo amps, with passive crossovers in place (also protects speakers), so I also didn't have to mess with gain matching and/or external crossover slopes. I'd much rather defer to the designer on anything as important as slopes/driver integration and driver interaction with the passive crossover components, and Bob Smith REALLY knows what he's doing there.
That being said, after I heard the SP Revelations with the Odyssey SE Mono's I can only imagine how nice 4 of them could sound. This would be truly ideal and you would not likely want for more horsepower and finesse at the same time.
If tube sound is what you're really after, though, that's a different deal entirely. I'll leave it to many others more experienced with the various suitable tube amps (like Bill Baker's Bella Extremes, Roger's RM's, George K's Moscode 401, among others) comment. I think it would be really tough to mix n' match and get it to work right.
I'd focus first on room tuning, treatments, or maybe source components first before I started along that path. Swapping amps for taste can be VERY expensive and time consuming. Having gone through a few myself (like Joule VZN-100's), I can really relate to this. You'd really have to be doing it just for fun, not worrying much about the transactions and costs.
Tom
