The sound card in the Mac Mini (first generation) sucks. It sucks very very hard. It has a single headphone jack for output, and even with headphones it's not all that good. My other (PC) computer, on the other hand, has a nice Audigy 2 card with 5.1 outputs. I'd really love to play music from my Mac, because I rather like iTunes. But short of buying an external soundcard, that's not gonna happen.
So, what I do is use iTunes for one thing, which is actually just about the only reason you'd want to use iTunes anyways: Organizing music. iTunes is very good at organizing. It stores music exactly as I'd always stored it myself:
../artist/album/songtitle. It also plays nicely with ID3 tags, so when you change the Artist tag on a song, it moves the song to a new artist directory. I still shudder to think of all the crap I used to go through in the olden days with Perl scripts and command-line ID3 tag editors.
Having iTunes organize the music, all I need to do is point Amarok on my PC to look in the "iTunes Music" folder on the Mini, and have it play over the LAN. I get the best of both worlds this way; I can use program in Windows, Linux or OS X as a "frontend" to the iTunes-managed music files, so long as that client stays read-only.