Tube/Solid State Bi-Amplification

Biamp capable speakers usually means there is a high pass filter behind the mid/tweeter speaker input and a low pass filter behind the mid/woofer speaker input. Adding an electronic crossover will mean that you have both active and passive crossover components operating together. -- I use a theme and variation of the tube/solid state approach with a tube amp running two-way floorstanders (bi-wired) and a solid state running a sub. The floorstanders are run full spectrum while the sub amp has an active low pass filter as well as volume and phase control.

The posts above give a good overview of what you'll need to do. Since some experimentation is now needed, it might be easiest to start with a Y-splitter for your preamp's output, then borrow some amps to try out a few combinations of passive biamping. The amps should have roughly the same gain/sensitivity but don't need to match exactly for these initial estimates of blending two "sonic personalities". In your case this approach is probably preferable to an active crossover, since it appears that your speakers already have internal filters (low or high pass) which allow each section to be driven by a full-range amp. But as mentioned above, you eventually might have issues with differing gain unless you introduce passive attenuation in the signal path.
I have been biamping Magnepan MG3.6/R speakers for a couple of years, and have owned or tried a number of amps trying to get the sound I want. I necessarily use an active crossover (Marchand, with level controls, xover at 250Hz, 24dB slopes). Tried many SS+SS combinations (even these can be tough to match sonically!). And I wasn't really satisfied with SS+tube for this speaker, although some people report success (search Planar Speaker Asylum). I ended up with a Llano Design Trinity hybrid amp (tube gain; transistor output) for the mids/highs on the MG3.6. The Llano gives me a tube sound but tends to blend well with my bass SS amp. I've now decided to get another Trinity amp for the bass, and fine-tune the character of each amp via its flexible tube acceptance (e.g. warm 12AX7 for the top and tight-bass 12AT7 for the bottom).

I'll agree that all of the above posts make good points. I have a pair of Magnepan 3.6s that I use with an active crossover. Fortunately, Magenpan provides you with the crossover points and slopes required in the active crossover. If you do not know what freq points/slopes you require, it could be tough to get it right. I chose the Marchand XM126 tube crossover. Mainly because it could be set up for the 18db 250hz low pass and 6db 200hz high pass crossover points. As for the results, having my CA-400 (SS) connected directly to the bass panels provided a more solid (controlled?) bass. I use a Cary SLA 70 (tube) for the top end. The top end really opened up for me and became even more detailed. Vocals were always great, I didn't notice as dramatic an improvent. Going active is a major step, be prepaired to fine tune for a while. It took over a month for me to get everything dialed in perfectly. It's almost like starting over, but the end result payed off.

The above posts are well stated. I would just add that Richard Vandersteen does not recommend "horizontal bi-amping" with his speakers. He claims that it is too difficult to properly integrate the bass with the upper frequencies. Vandersteen does recommend passive VERTICAL bi-amping though. Good Luck. Craig

Thanks to everyone for generously volunteering your experience and expertise. You've really helped clarify this issue for me.