Active crossovers

There are serveral good active cross overs. Bryston 10B and the Marchand are the two that both reasonably priced and sound very good. They are both solid state. I bought the Bryston--at the time Marchand did not make a balanced cross-over. I'm pretty sure they do now. As to tube cross-overs, I can't really comment. I know of a few, but have not heard them. As to your "Stupid Question", it's really not a stupid question. If your speakers are designed to be actively crossed over then their response and impedance curves should be reasonable enough that it will not cause a significant change at various levels. However, if the two amps are not reasonably well matched in terms of sensitivity and possibly more importantly their current delivery (depending on the speaker), then you could wind up with a problem. I have not experienced this problem, but my differential between high and low end is only 1 dB. The Bryston only allows a +/- 5 dB, and this may be the reason why--if it were more you could run into some non-linear problems as you suggested.

KP: There is a filter prior to the driver. It is effectively the cross-over. Essentially a high pass for the highs and a low pass for the lows. As Sean points out, you should bi-pass these. However, there is a word of warning here. While the cross-over is reducing the benefit of active bi-amping, these filter networks can be part of the voicing of the speaker. Eliminating them may change the characteristic of the speaker--sometimes for the better, but depending on it's design it can be for the worse. This is an area where I would contact the speaker manufacturer and ask them how (and even if) they recommend active bi-amping. For some speakers active bi-amping just won't work very well, but I'm not familiar enough with yours to know whether or not that is the case.

The Marchand is quite good. Some have indicated it's better sounding than the Bryston, but I have to admit I have never done a direct comparison. I think it's fair to say that $ for $ it's probably the best out there. If your budget allows for more, then it's difficult to tell which unit is best. As to the Krell, they did have some 60 Hz noise problems at one time. Perhaps that has been fixed, but if I'm not mistaken they quit making the KBX some time ago and getting the boards for the various cross-over points might be difficult. You should look into this carefully before going that route for sure.