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 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).