How do I bi-amp using NuForces and tubes?

The Jolida will work but, since you are using it only as a potentiometer, why not just add a pot to the higher gain amp?

Kal

The gain on the Cary V12-R is 1.3V pretty high, you will have to add a volume pot in front of them, you can use this:
http://mysite.verizon.net/vze4c5pt/id2.html

I also reccomend a Line Level Passive XO for the Cary amp, you will get much better response if you limit the bass response!!!
You will loose some gain, which could actually help to match up with the nuforce amps!!
Do a search on Biamp here there is a big thread with lots of tips

Do Biamp, you will not get better results by changing gear!!

"How will you balance the two amps for gain?" That is THE question. What are my options for doing that? Would something like a Jolida model JD 50A work? Other suggestions? - Steve

How will you balance the two amps for gain? Odds are, they are different.