YMMV of course, but I've routinely had two main problems with using a computer as a music source:
- USB ground loops
- Power supply noise getting into the AC line.
My experience with Mac's, and any computer really, is the power supplies tend to inject a lot of noise into the system that's almost impossible to clean up.
I have no problem with a computer being used as a source, but not on the same AC circuit.
Also, inexpesnsive USB isolators can really help if your DAC is happy with them. It's a real shame 100% of DACs today don't have 100% isolated USB interfaces but it still happens.