CALLE Works as described, for free. Well done!
It's the only app I use in Rosetta though, an Intel-release would be appreciated. Also I can't get it to put the converted files in the designated folder - they appears in the origin folder no matter what I do, but it's not really a problem - and it would cut one step in the process if it would encode FLACs to MP3/MP4 instead of just AIFFs (I know, I'm more of a diskophile than a discophile).
(Version 1.1)