Some software may require you to decode the FLAC file into another format. For Macs we recommend AIFF files. This is an uncompressed CD-quality (or higher) file formats and can be burned directly to audio CD, or compressed (should you so desire) into any other file format for transfer to an iPod or similar portable media player.
xACT stands for X Audio Compression Toolkit. Amongst other things, it allows you to convert FLAC files into CD-quality uncompressed AIFFs so that they can be played back on a Mac in iTunes (or other software).
The application gets 5 stars out of 5 at Macupdate.com and is recommended by Pristine Classical's Mac users for FLAC and iTunes integration:
"Select 'AIFF' in the 'decode' tab and 'Music' as the place where you want to download for storing/opening and the converted 'FLAC' promptly goes direct to 'iTunes' where you can play in either 'Music' or (of course) 'Recently Added' (which is where you'd do any burn)."
Test your FLAC conversion with the following piece of music: