Can you explain?
Yes, I’m not *exactly* sure how you have your stuff set up. It sounds like perhaps you have your ~/Music directory connected to your mini, and Firefly running on your mini. If so, then that will work.
Generally, Firefly just looks in ~/Music for music files, so as long as new files get thrown in there, it will be happy.
The warning about purchased songs is that the soundbridge won’t play files downloaded from the iTunes store. Neither will *anything* other than iTunes/iPod, as far as I know.