How can I improve Apple iTunes through my system?

Awesome! A bunch of Mac users, G5ers to boot!

Check out stereo-link.com

First off, be weary of any ma-audio cards as they dont work in the g5's pci-x slots. Second, make sure your processor performance is set to auto or choose for me in energy saver panel as it will keep the fans dead silent. I would look at a monarchy audio or audio alchemy jitter filter, they will help as the digital out is so much better. Try connecting the g5 to a power conditioner or the same ground as your stereo. If the serial ATA drives get to loud then try a external firewire drive that you can place out of the way. I have also had good luck with placing a older gigabit ethernet g4 in another room and running full gigabit to the g5, do not really have any bandwidth issues for movies or music and don't hear the 10k scsi drives spinning away with the g4.

pe3046, it should be noted that the entry level g5 has pci, not pci-x slots. The other 2 models in the line up, as you correctly stated, have the brand new pci-x slots.

Brimac, there is still an issue with the pci slots in the entry level G5 since it only accepts 3.3 volt cards. Also the G5 is very quiet, espescially compared to late model G4. It can sit in the listening room and not draw any attention to itself.