So I broke done and bought (for a song) a Xbox 5.1 Surround Sound System:
http://www.xbox.com/en-US/hardware/51surroundsound.htm
It's connected to my PM 2.7 with a digital optical cable and I've been loving all the 5.1 goodness (and just having great speakers.)
The one catch is the lack of volume control from the keyboard. The volume up and volume down don't work for the speakers, but mute does. It's really frustrating to adjust the iTunes volume from within the program.
Is there a software solution?
Should I be connecting a different way? The speakers have five audio inputs: Two Fiber optic digital, one coaxial digital, one analog RCA, and one USB 1.1 device port.