I am not a fan of FLAC because the SQ is inferior to .wav. I don't care if you cannot hear the difference. I can hear the difference.
Changing FLAC to wav with XLD is the best on Mac. Free download. Google it.
dBpoweramp and XLD are perhaps the most popular. XLD is free. Convert your files to aiff or alac. Keep in mind if you choose wav it doesn't support metadata like other formats.
The age-old wav vs flac debate has been raging for years now with strong proponents on both sides. Listen for yourself if you care to. While I respect Steve's viewpoint I don't agree with him and I assume he won't be the one listening to your system.