Pete,
You will need to check your owners manual to see if the Surround Back channels can be reassigned to output the Front L &R channels. However, I think the next generation SR805 offers this and not the 804. Regardless, this is known as 'passive' bi-amping and there is advantage or improvement in sound/clarity while doing this. You are still utilizing the speakers cross-over network...In terms of true bi-amplification cross-over and amplification is all done from the speaker externally....