How to balance tube on top, solid on the bottom?

Many pro power SS amps have sensitivity pots (my Bryston 4B does). You can adjust these to match the level in your tubes.

Biamping is probably only worth the trouble if you eliminate the passive crossover in the speakers. I hope you are planning to do this or it will be a lot of work for only modest gain.

This link explains more http://sound.westhost.com/bi-amp.htm