Bi amping with Tube and Solid State

Fortunately, I have gain control on my McIntosh. According to Jeff, you said go one way or the other, do you mean all tubes or all ss??

Try it - I biamp my Legacy 20/20 Focus with tubes on top and SS on the bottom. Sounds good. If you do not like it than undo.

This is what is known as "Fool's Bi-amping"!! It's bi-amping for the sake of bi-amping. While it is true that you might reap some benefits, the hassles of making sure that high & low are matched is perhaps not worth the time & additional expenditure of cables.
It would be much better to get a very good external xover ckt. This will keep the low freq. out of the high freq path & ensure that the high freq amp is only responding to the signal it really should. This will also keep the speaker cones from mistakenly responding to the low freq. signal, which could cause smearing. Similar argument holds for the low freq amp & the woofer driver.
If you have a volume control on the McIntosh that will help a lot but the tone of the ss & tube amps might be very different. Thus, even if the ss amp gives better bass control you might not like the tone diff.
Just MO, ymmv. fwiw.

I am biamping, with great success, my MG3.5 with ARC VT100 MKII (tube) on the treble/midrange and Kenwood L07M (SS) on the bass panels.
I am using the Marchand 126s active crossover. For proper blending I am using 250 Hz @6dB/Octave for the high pass and the low pass at 200 Hz @ 18dB/octave.

It is incredible how people on this forum can make such sweeping, and incorrect generalizations without clarification.

If you ask Linn they will stand for product against removing built-in crossover and they're partially right. On the other hand passive bi-amplification of even perfectly matched amps can drive system out of tonal balance. Volume control in your Mac might help matching but will not help to keep balance due to the complexity of a speaker load connected to two amplifiers.
Without worries you can do it with electronic crossover $500...$1000.