Hi!
Not many hi end amps out there with volumes....
One suggestion would be to find a remote add-on, then you can use any amp you want. There are two that I know of - Creek makes a good one for a couple hundred clams, and if you can find one, Chase Technologies made one that you still see around on ebay or online outlets very cheap - $50 or so. I have two of the Chase units, use them in my 5.1 channels home theatre set up so I can run direct out of the DVD player into the Chase(s) then into my Aragon amps without having a receiver in the loop. They are nice and transparent, if used with decent interconnects.
However, let me also say that I have never heard a bi-amop set up using two totally different amps (especially tube with transistor) work satifactorily. The discontinuity between the two amps makes speaker integration nearly impossible, and this is clearly audible.
Good luck!
James