Does biamping w/ SS + tubes work?

Biamping with two different technologies can work well but it's a great deal of work to get the right combination. Even if you do get it right, amps work at different speeds so you can usually detect a slight blurring.

I agree with the people that told you it doesn't work well...emphasis on "well" not "work". It will work well at the outside freqs and likely not so much where they cross over. If you do go this way, choose a ss amp based on how much you like the mid/upper range as well as the bass. That will give you the best chance of messing up the "least" in the important midrange area.

I'm not a fan of passive biamping. Give some thought to going the active x/o route. You have 3 really great amps. You may find out that when you direct couple one of them to a woofer the bass may surprise you.

Another point: Are your amps up to spec? They are pretty old and if their caps are weak, they will not do bass very well. Good luck.

It usually doesn't work well, but with some careful choices and work it sometimes can. Though there are exceptions, typically I wouldn't recommend it.