I haven't been using my stereo much for several years, I don't understand components but I do appreciate well reproduced music. I recently read about connecting a usb dac and running my music from my portable computer which would be a great setup for me. I presently have a NAD T 760 receiver, Mission 773 speakers and a G4 ibook. I need to buy a DAC and whatever else makes sense to make this work. Any suggestions?