It's a pointless idea.
Tim, that is not my experience... and I know others who would also disagree with you.
One difference on my setup from a 'server'... my DAC is inside the computer, mounted on the digital portion of an ESI Juli@ sound card. Both the soundcard and the DAC have their own power supplies and are not powered from the motherboard power, so they share grounds, but no power with the computer.
I originally used a supply with two 12v linear sections, one directly feeding the processor P4 plug, the other a PicoPSU for the 20-24 pin main ATX power connection. Now I have a fully linear supply, 2 12v rails, 2 5v rails, and 3.3v. Yup, as Paul says, it takes up a lot of space... about 4-6x that of the original computer SMPS. And it is much more inefficient and produces a good bit of heat (like these are serious problems for us who like tubes!). And I agree with Paul that choke-filtering is the way to go... planned for my next iteration, but it gets a lot bigger then and I have to replan my music player's packaging. It does have soft-recovery diodes... lots of them! These are key to the sonics, as are good regulators. And also, I did have to deal with computer turn-on sequencing and signaling, although that turned out to have some simple solutions.
I do know others who have done either hybrid linear-PicoPSU or fully linear supplies with SPDIF or USB-connected DACs and also found it worthwhile sonically. I've even know of battery-powered setups, but that's even beyond where I'll go... at least for now.
Having done this, I can say without any question that it is worthwhile if you want the best sound from a computer music setup, whether using the output from a DAC inside of the PC or an SPDIF or USB-connected one (whether it is powered by the USB buss or separately powered). The only setup I might expect it not to matter is when one has an ethernet-connected server to a player like a Squeezebox.
And to do a supply with a single 12v rail for the motherboard recommended for the CAPS V3, it would be a snap!
My suggestion... try it before you say it doesn't make a difference!
Greg in Mississippi
P.S. The attached picture is of my music server's linear supply during development. It got a bit more complex (and uglier!) as it got to its current, fully-operational state. It has been running mostly 24-7 for the last two years, so reliability is not an issue.
