I cannot speak for the Audio side of your needs, and if your photography is not cutting edge, consider the dual 2.0 G5; the models that can take up to 8 GB of Ram.
I'd seriously consider this option if you already have CS2 Photoshop or the Creative Suite from your previous computer purchases. Tiger for this would be great.
Sure the new Intel Mac Pro is faster, but seriously, how much do you need this kind of speed if you are learning Photoshop and it's you, the user, that is the slowest part of your workflow. I'm putting 300mg Tiffs through some simple edits and I am very pleased of the G5's speed compared to my 1.2 G4. Load it up with inexpensive Ram and you'll be surprised. Based on my own modest experience, a 30" monitor would speed my overall workflow more than a faster, new computer. Sometimes its the human factor of moving things around on the screen that gets me bogged down than how fast my actual computer is. However, a video card that can handle a 30" monitor are getting tough to find.
People are dumping their G5s to upgrade. Hurry, the deals will only last so long before the recession overtakes us then we're all stuck with the machines we have heading into the recession.
If you don't have the software, and cannot find an inexpensive copy of CS2, then my thoughts would have to be reconsidered. For me, already having the CS2 software, Corel Painter, amongst other packages, getting a used G5 for $1,000, and not paying any sales tax was a great value in savings over a new system. With buying a new system, I would have also had to upgrade to CS3 and that pushes the cost up another $800 ontop of a new machine.
It's a tough call. Only your needs and finances can dictate what you should do.
Mike