What are some of the things to know about biamping? I am considering this but do not know very much about it.
I need info on the active xover and what not.
Jsman, i bi-amp and for various reasons it seems right for me.

bi-amping is when you are using 4 channels of amplification for stereo instead of two could be one amp with 4 channels, 2 stereo amps or 4 monoblocks. i assume that your speakers have two sets of speaker for the midrange and tweeter and one for your woofer.

bi-wireing is when you use two sets of speaker cables out of one amplifier. these two sets of speaker cables are connected to two different sets of binding posts on the speakers.

it would help to answer your question if you could explain the context of your system. which speakers, ampifiers, preamp and size of these things affect what the best approiach might be.

you mention active xover; do you now have one or are you considering one? this direction is a whole additional issue. the whole connectivity question depends on your system configuration......are you running a single set of interconnects out of your preamp into this active crossover or are there two sets of preamp outputs on your preamp so separate sets of interconnects can be run to all 4 channels?

in general; you want the same amps for all 4 channels and the same speaker cables but beyond that there are lots of considerations and viewpoints on the best solutions.
My system includes, Sophia Electric 300b MKII power amp,
which I want to use on my tweeters and mids. Pre Amp Rogue
Audio 99 Magnum, one set of pre outs. Marantz 300DC power amp, which I want to put on the woofers. My confusion is about the active xover. Can you help? I do not have one yet.
If anyone is interested I have drawn-up 6 illustrations of different bi-amping options. Some illustrations are with an active crossover. I really did it for my own understanding, but if you would like them I can send them to anyone. They were drawn in Autocad, but I will send them in .pdf format unless you have ACAD. Pdf's require adobe reader which is available free.
I use a Outlaw ICBM to combine SA220's (monoblocked) to woofers, mid/tweeters with a ML9. Seems to work fine.
You need a crossover to equalize the gain/volume on differant amps and set your crossover freq/slope.
Just gives you more toys to play with.
Jsman, thanks for the info. please tell me what speakers you have and the approximate size of your room.

using an SET amp combined with a solid state amp will be tricky...but do-able. there are many that do take that approach.

personally, the approach i might take would be to use some sort of 'Y' splitter with one amp simply attenuated with a passive volume control such as the Placette RVC which will be transparent in the signal path. this would be much simpler than any active crossover design and with amps of that level you will hear it. an outboard crossover can yeild some advantages by not sending the entire bandwidth to the SET but IMHO at too great a price (both $$ and sonically).

there are impedence issues which are beyond my personal level of expertise that you could run into when using a splitter and a passive attenuator.

your amps are both quite special and if properly combined should sound great.

maybe someone with specific SET/SS biamping experience can chime in with other suggestions.
MikeL makes some great points. I use two EVC ultimate attenuators in my biamp setup.

But I think in this case it really makes sense to go for the active x-over since you really do want to filter out the bass freqs going to the 300b SET amp for the tweets since your available power is fairly limited.

That should increase your dynamic range allowing for higher max SPL.
If going for the active bi-amping the thing you need to keep in mind is the woofer x-over freq and the slopes of the high/low pass filters of the speaker's built-in x-over. What type of speakers are you planning to biamp?
I am sorry guys that it took me so long to get back to ya.
I have klipsch khorns for speakers, so power is not really
an issue. It's more about what I need and the options I may have. Thanks for all your help. BTW my room is small.
K-horns are so efficient there is really no advantage to bi-amping them. The woofer only goes down to 32 hz in the right room.
Jsman, in specific those speakers will probably have little to any positive reaction to bi-amping,, definatley save the money on buying a processor and additional amps and put it all into a better standalone 2 channel killer amp. You want more power or bass, go with a newer mcintosh solid state and it will nearly sound like tubes, but with rediculous power for the bottom end on that 15" woofer.. I use to own these combinations ...