B&K Bi-amp question

On my B&K AVR 507 S2, I've tried to bi-amp my speakers using the zone 1 and 2 amps. My 507 is set up with the 2 rear channel outputs as zone 2. Using each zone to bi-amp seems to work OK except that I can't control volume simultaneously. I have to adjust zone 1, then go to zone 2, and change that. There are quite a few steps in getting from one to the other. It seems to me that I should be able to set it up so that they work together. I've set zone 2 to turn on with zone 1 and use the same input as zone 1.
Anybody know if this is possible? Thanks,