Tube amps and low impedances

yes it definitely would

You've definitely got it, Mitch!
I think what is impossible to acheive with one amp let it be ultra-mega-priced one is possible to acheive with mix of tubes and solid state in bi-amplification.

Biamping with a mixture of tube and SS is a thought, but perhaps not practical for sonic performance. I can think of three factors that will affect the sound:
1. You need to match voltage gain (meaning matching volume will be a problem).
2. You need to match input impedence (meaning you can't use use a y-plug to double the input signal and expect good result).
3. You need to match phase coherence (e.g. some tube amps are 180 degree out of phase, which will cause lots of fun at the crossover region, and as well affecting the sonic presentation as a whole).

Tube amp and SS amp are particularly different in # 2 and #3. If you are willing to make the compromise, why not considering a hybrid amp that uses tubes to handle the voltage amplification and transistors the current? The result should be better (IN THEORY) than mixing tube and SS in a bi-amp configuration.

hcheu, aside from the Musical Fidelity Nu Vista and Tri Vista, what other good hybrid amps are there? I too have thought about bi-amping with tubes and solid state but it sounds too complicated to be practical.