As Noah said, bi-amping with a pre/pro is easy, just split the output signal and run it into two separate amps. This too gets much closer to what you want to do with bi-amping, if each of the amps you're running into has it's own power supply. Unlike the amps built into a receiver which all draw from the same power supply; where bi-amping offers a dubious improvement.

What mdrconsult may be talking about is the multi-zone support. If the 6th and 7th channel of the 997 can be assigned to zone 2 and then connected to their own amp in another room that also could be advantageous (provided zone 2 can be from digital sources, and not just limited to the analog inputs as so many receivers do).