Is it going to be a usb dac? You will want to look for performance on USB and power supply. The alix uses compact flash card, cheap. Doesn't need much storage to run so no need ofr something bigger like 40gb with that setup.
Also, should mention, some people were using linear power supply from parts express as cheap but decent power for the Alix.
I am not very experienced, I am sure others will give you better input...