My first post then...
I think your audiophile friends don't understand how digital music works. A couple of reasons why (in my own opinion) the PSU and other no audiophile bits will have no effect:
The computer PSU is operating at a very high switching rate (should be way beyond the audible range), AND is enclosed in a farraday cage (the metal "box" that covers it). You will therefore have no interference either directly or through electronic radiation.
In a digital stream the only important bit is indeed the "bit" which is stream of 0's and 1's (or " 0 volt" and +5 volt" if you want). No matter how exotic your components are, when it comes to digital streams they have no means of altering this stream. Sure, a variance in a resistor could for instance change the 5 V to say 4.5 V, but as long as it isn't 0 V, there is no problem!
Even if you were to inject through whatever means, wrong "bits" into the stream, or manage to remove some, there will always be some sort of checksum to ensure that what was sent by the computer is received correctly by the DAC.
