Fred,
I love my headless Mac Mini, I control it via my laptop using screen sharing, and there are some great audio players out there for Mac. Both Pure Music and Fidelia are great and reasonably priced.
When I had an EE DAC, the optical didn't always work great with my Mac Mini (an older model). I think that this is because my Mac Mini has some fairly nasty jitter on the optical output (not sure if new models improve on this, but I have also read that outside the first generation of Apple AirPort Expresses, the subsequent Airport Expresses have high jitter issues as well). IIRC, the Sabre chip can be pretty sensitive to jitter. So I would recommend going with a USB-SPDIF converter. With the EE DAC you could use an M2Tech HiFace, with BNC no less. I did that and it worked great. Other more recent converters that have gotten good reviews are the new April Music converter (see the 6moons review) and the Audiophilio converters (also reviewed at 6moons IIRC). And there are others from Musical Fidelity, Audio gd, etc. A number of solid choices at different price points it seems.
But I do really love the MacMini interface options for playing my digital files.