Brad,
That all depends on how much you want to put into each approach. Right now, it seems the mac mini approach has more potential, but at somewhat greater cost. A digital modified sb touch with a decent linear psu and either the soundcheck mods or the relatively new EDO plug-in is a very nice solution -- for coax, usb, or optical.
On the mac mini (or PC) side, the quality of the power source and the usb->spdif converter will be a major factor, or at least that is the general idea -- buth with John's receiver tricks, that may play less of a role.
I'm also working on a linear PSU that I think can be built for somewhat less than $200 (maybe even slightly over $100) that could really be very nice (and no need for bybee music rails, etc. Unfortunately, with the pending move and getting resettled, the timeframe for this project is completely unknown, but hopefully before the end of the year.
HTH,
Jim
Jim Rebman -- recovering audiophile
Equitech balanced power; uRendu, USB processor -> Musette DAC -> 5670 tube buffer -> Finale Audio F138 FFX -> Cain and Cain Abbys near-field).
s.e.x. 2.1 under construction. Want list: Stereomour II
All ICs homemade (speaker and power next)