You could try the HAGCLOCK, it certainly runs very well at 12MHz, but the issue is that it requires two supplies you don't have. In order to isolate computer and audio system grounds, the HAGUSB uses that very expensive output SPDIF tranny. And the USB only has 5V (kinda dirty, which is why it gets filtered and linear regulated down to 3.3V).
So to do this, you would have to add a +/-12V supply referenced to the power supply ground, and completely isolated galvanically from the audio ground. Very possible, but it takes a bit of work.
jh