bi amp imrpoving?

"Keep in mind that it is not REALLY necessary to bypass, or delete, the existing crossovers in your speaker system, to experience most of the benefits of active biamping."

For MOST of the benefits of bi-amping, yes it is necessary to go to an active crossover. For one thing, by connecting the drivers directly to the amplifiers the speakers present a nearly perfect resistive load, which is much easier for an amp to drive. Bi-amping via passive crossovers has some benefit, but using an active crossover puts you in another world as far as engineering benefits.

Active crossovers are seldom used though, because an active crossover costs A LOT more to build than a passive crossover, you need multiple channels of amplification (perhaps as many as eight for two speakers), and it's better if the amps are engineered to the speaker system, with more watts in the lower frequency connections, etc. All of this conspires to relegate 99% of commercial products to passive crossovers, which are inferior.

"Hello Simon,
For an amplifier with two outputs on each side (such as the Spectron), is there a theoretical or actual advantage to using one output for the low frequency drivers and the other output for the high frequency drivers?"

I'm not Simon, but there's no way the answer to your question would be yes. That's just bi-wiring, and if you are using a single cable of sufficient gauge there's no advantage to bi-wiring. (Apologies to those that believe otherwise.)

"Would the use of a single amplifier with megawatt output, used with medium-efficiency speakers, negate any possible additional benefit of biamping?"

In almost every case, yes.

Psag, that's different. I thought you were referring to passive bi-amping. IMO, active bi-amping can be big win, and a single megawatt amp with a passive crossover have to be of *very* high quality to compete. I think we always have to preface questions about bi-amping or multi-amping with whether we are referring to the active or passive case.