You must be referring to the Clip+, because I'm pretty sure that the Clip Zip handles flac and alac files:
If I am understanding you correctly, if you install rockbox on the Clip+, then you can also play flac and alac files. If that's right, then that's great!
Oh thats cool it does flac. But not alac. Rockbox says they support alac. I was talkin about clip+ but neither do alac unrockboxed.