iTunes will not play FLAC but there are converters that will convert FLAC to AIFF or ALAC. XLD comes to mind and works via a GUI or command line. I haven't used it in years. You can batch convert but be careful... experiment first with source and destination directory, and keep a copy of your original totally separate in a safe place while experimenting.
I played with HQPlayer but hated the library management interface. It was clunky IMHO. HQPlayer can also be a CPU hog depending on the upsampling you choose.
I played with BitPerfect a few years ago and it locked up intermittently so I figured it wasn't ready for prime time. I haven't played with it since but I would expect that it has been fixed by now.
