Here's what I do:
- Open Toast and choose audio CD.
- Add the FLAC files to Toast -- note that you must have all the tracks that were on the original CD.
- Use Save As Disc Image to create a .sd2f file in Toast.
- In the Finder, go to the .sd2f file, Control-click on it, and select More » Mount It. If you don't have this entry, then you need to get Toast to install it for you; it's in the preferences.
- In iTunes, the CD you just mounted should be recognized and the track list will be found from the CDDB.
- Import the songs into iTunes using your normal settings, and all the tags will come from the CDDB info.
- You can now eject the CD and delete the .sd2f file.
The only thing to look out for is to make sure you have the right number of tracks. I also set up Toast to use a zero-second gap between tracks, as this works best for me in iTunes.

