I know a couple of people that use the Ultra-Fi ECM in their MAC Mini based digital rigs and they feel it is a tremendous upgrade. Here's a link to one that is currently for sale. I'm not affiliated with this seller (don't even know him), but I do know the manufacturer and a couple of his customers who use the ECM. I'm not endorsing the product as I haven't heard it yet. Just passing along some information......
http://www.audiogon.com/cgi-bin/cls.pl?powrcond&1284048765&/Ultra-Fi-ECM-music-server-cond
http://www.audiogon.com/cgi-bin/cls.pl?powrcond&1284048765&/Ultra-Fi-ECM-music-server-cond