Honestly, I think that "voice-matching" your surrounds with your fronts is far more beneficial than bi-amping all around. Some people think that sounds which are emitted from behind you are less important than sounds that are coming from in front of you. Kind of a mistake.
Once I got all my 5.1 speakers to match (all vintage JBL, Cabaret series, custom made by my own hands), it just seemed as if everything just got easier and the dynamics were/ARE amazing and I never run out of headroom, even when playing at headsplitting levels.
With my system, I can only bi-amp the fronts and it DOES make a difference