Fatparrot, yes, I had an ARC amp that had input trim pots which I never used but I have to imagine that the quality here is not very good. I would really only want this on my low-frequency amp ... and ultimately it might be the high-frequency amp that needs to be attentuated.
Yes, when you actively biamp, the idea is to remove the speaker's crossover. But this implies an active crossover between the line stage and amp. The advantage of this approach is that you eliminate the poor quality inductors and capacitors that are typical in a speaker's crossover.
In an active crossover, no inductors are needed at all. Another benefit here is that there is often an increase in the speaker's efficiency because of the loss of signal caused by the speaker's crossover. But a problem here is that any poorly implemented active circuit between the line stage and amp can so easily result in the loss of the incredible harmonic richness and 3-dimensionality that some tube-based systems exhibit so well. I am looking to do this in the next month or so with the Space-Tech-Lab tube crossover with tube regulated supply.
Check it out: http://space-tech-lab.com/
If the idea is strictly to have the line stage drive two amps, each amp then driving a stage of the speaker's crossover, you are still biamping but using a passive crossover (the one in the speaker). This latter method is very popular in the UK where just about every speaker has the two sets of terminals (for high and low freqs) and a shorting bar to use only one amp. This is what Quincy above has described.
Hope this helps.
John
