Haven't got the MAC Mini but maybe my experience is relevant to the enquiry. Recently bought an iMac with Airport Express (as a starting point to replace a Lyngdorf CD player). CDs are converted into ALAC format.
After a 'Camp David' level of deliberation the Rega DACs apparent fine combination of price/performance got it selected as Airport Express replacement. Initially I used a USB connection from the iMac and there was a useful step-up in performance, but no cigar though. The iMac USB is limited, I believe, to 44.1kHz but don't think this was the hold up. Then replaced USB with S/PDIF - aha! Now the system was finally singing and in comparison with the CD player was well-ahead in several areas, notable being overall timing and bass (obvious with piano). It seems that when connected via USB the Rega DAC probably doesn't have the raw performance of the latest async. DACs (to be expected, in fairness) but if you can live with S/PDIF then the Rega seems to perform extremely well (in my system context). btw the Rega DAC did take a day or two to bed-in.
Have now added Pure Music - excellent. And at 88.2kHz and with memory playback it's hard to know if further improvement is sensibly possible.
Next is to add either USB or network storage for my iTunes library. I would expect neither to detract from performance when using PM's memory playback mode - comments on the best approach welcome though.
In conclusion the SPDIF from Mac to Rega DAC provides a very pleasing result to my ears.
