Dolby EX and other 6.1 systems add a lot to the envelopment of the surrounds, even when decoding movies that were originally mixed in straight 5.1. I would go this route if you can swing it.

Bi-amping (passive) is essentially useless as it does not do anything electrically that simply using larger gauge speaker wires would do. If your amplifier has adequate damping factor (the Outlaw amps do) and your speaker wire is large enough (12 gauge or larger), then there is absolutely no benefit for passive bi-amping. Any improvements that I have heard people talk about have mysteriously vanished when they had to listen to the system with a blind comparison between passive bi-amping and with a regular single amp hookup.