Hi mark, thanks for the welcome and quick reply!
I've done some fooling around with Audio Midi Setup with khz, bitrate, and faders, and also got rid of a couple random things running in the background, to no avail. Here's my activity monitor on startup (plus Firefox, Activity Monitor, and screen capture):
http://img93.imageshack.us/img93/1844/59596146.png
I have tried a few players (iTunes, Cog, Songbird, Play) and the problem is there with all of them.