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.