In most cases--yes. Generally speaking, on-board sound is not so good; generally better with a Mac. You can also get a quality external DAC/Amp (desktop or portable) instead.
Your 320 MP3's are OK. Higher quality file formats or CD's with well recorded tracks are even better.
Thanks for the input!
Hmm, interesting. Perhaps I'll just send my old headphones in for repair (they need a new cable) and buy an amp, and hold off on getting new cans for the time being.