If your music files are in an iTunes library on a Mini, then you can sync from it directly to your phone, and set the level of compression you need depending on how much music you have to sync.
And if you're running a recent version of iTunes, you can sync wirelessly, which is what I do with my iPhone/Mac Mini.
Maybe this link will help you.
http://support.apple.com/kb/HT1386Sound quality is really a function of what you are using to play the music -- the speaker in the phone, headphones, streaming to stereo, etc. What are you using?