On Rotel products with a PC-USB rear panel input, you can play any file format that is supported on the computer. So to play FLAC files for example, just connect your computer to the Rotel unit via the PC-USB connection and play the files using any media player software that supports FLAC, such as VLC player.

You could also play FLAC files from an iPod/iPhone connected to the front USB input as well, if that phone has an app that will play back FLAC files.