If your ready to invest in stand alone cross-overs, bi-amping does wonders. Bi-wiring on the other hand is a debate. Some think it does wonders, others don't. I bi-wire my fronts only because I can.

I do agree with JohnK however with respect to your current amp. NAD's stuff puts out plenty of power for most applications. If you went with a big-ass amp you would notice a change in overall DB and depending on what kind of amp you went with, the amp itself may bring a few of it's own characteristics to the table.