I use Fidelia, but the cheaper version, ($20). Works fine with a lovely interface. It just uses iTunes as your library but plays and converts if needed without any hiccups.
I also use BitPerfect. Even cheaper, ($5). But you retain the iTunes interface. The only issue with BitPerfect is that it's not Airplay compatible.
I also use BitPerfect. Even cheaper, ($5). But you retain the iTunes interface. The only issue with BitPerfect is that it's not Airplay compatible.