My very strong suggestion is to simply get dbPowerAmp and be done with it.
it has supported converting 24bit FLAC to ALAC (Apple Lossless) for almost 2 years, now. It'll have no trouble decoding to AIFF, if that is what you need.
It is a swiss-army knife for audio conversions. I bought it, it works so well. It supports multiple cores, so if you have a Quad Core processor, it'll do 4 files at a time.
I did the whole Beatles 24bit catalog from FLAC to ALAC in about 9 minutes flat. 200+ files. The tags transfer, as well (assuming your destination format supports tagging).
Just get it, and never have to worry about any of it again. Even does ripping in secure mode. I have definitely had my money's worth from it.
http://www.dbpoweramp.com/dmc.htm
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