How can I improve Apple iTunes through my system?

How can I improve my new Apple Macintosh G5 playing iTunes through my Linn sound system?

Can I bypass the volume control on the Mac so it feeds line level to the Linn system?

I also have iMac and PowerBooks that I would like to do the same with.

I import my CDs as AIFF uncommpressed files.

Sound quality is of most importance, not price!
I would recommend either a high-end sound card, like the ESI U24. It's external USB and works with MACs and PCs. The other option would be to send the SPDIF signal to a high end DAC. The later would probably be the best (you can spend a good $10k on a DAC if money is no object) but the ESI cards are very good.
Go to preferences and turn off all the effects. Leave the volume control on the main screen all the way up (to the right) and don't change the volume or add EQ for individual songs by using the Info/Option control. Since the G5 comes with a built in optical digital out, you should connect it to an external high quality D/A. If you want, you can add a jitter reduction device between the G5 and the D/A.
Awesome! A bunch of Mac users, G5ers to boot!
Check out
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.
My wife and I went to see my Grandparents in Albany Oregon, just two weeks ago. We drove to Corvallis and took advantage of the 'no sales tax' in Oregon and bought a G5. The middle model. The saved sales tax got us a really nifty digital camera. It had not thought to use my G5 as an audio source, although we don't have a high end audio feed in our computer room.

Thanks folks. Interesting thread.
You obviously have a great investment in your Linn system, so if you want to incorporate your new Mac G5 as a digital music server front end to your Linn system, get a Lynx Studio Technologies Lynx 22 which has balanced analog I/O and S/PDIF digital I/O. Depending on what you prefer, you can send the signal into your Linn control amplifier from the analog outputs, or into your DAC (if you have one) from the digital outputs. Most professional audio engineers love the Lynx products for their quality AD/DA processors which rival those of much more expensive outboard DACs. Lynx offers Mac OS X drivers as well for the card (i.e., full Core Audio compatibility). The Lynx 22 and its slightly more expensive sibling, the Lynx 2 (Version B), contain internal clocks for reducing jitter distortion and for creating a clear and deep soundstage. These really are great bargains when you think of the audiophile performance you can extract from these devices. Together with your Mac G5, you'll have something far superior to Linn's Tunboks.