Bi-amping

read my initial comments.

Cheers, I think I was bogged down by the alternatives, which now, I have realised does not apply or answer my ambiguous question. Thank you all for your replies.  

Active bi-amping is obviously the best eliminating the passive elements in the signal path (big coils mainly, and caps; in some cases resistors). 

But even PASSIVE bi-amping can have significant benefits. 

Example: the 2 coil bass of my Infitiy Quantum 2 dips below 2 ohm impedance and requires very powerful and stable amp. Yet the same amp has to drive the EMIT planar magnetic tweeters through the passive crossover. By 'splitting' the task, a poweful (but not very 'sweet') brute amp (class A/B, maybe even a class D) can be used for the bass (200 Hz crossover), and a better sounding but less powerful (class A? maybe even tube?) amp for the low mids and highs. 

Kraft,

That's a great idea you made. They might consider an amp with a volume control on the upper amp so they can level match the powers.