I would also suggest Full Compass. From what I've been lead to believe on the Audio Asulum boards, you'll have an easier time calling them, than trying to find the unit either in their catalog our on their website.
Full Compass is also reported to have the "best price" on this unit.
Strangely enough their catalog does not have a "DAC" section, like an audiophile would expect. If I remember correctly the A.R.T. DI/O was in a section that wasn't intuitive (at least to me).