It was the dynamic art tagging that was messing up alac streaming to the roku. My note to RokuMike:
Fixed it. The problem was I had art_filename set to folder.jpg. For some reason mt-daapd thought it needed to add the album art (which it didn’t because it is in the m4a tag). It messed up the file by doing so – the alac files were fine until mt-daapd futzed with them. Commenting it out of the conf file fixed it.
Note this is unrelated to the fast start info issue which some alac files have.
Ahhh… interesting. Apparently iTunes is more tolerant of hosed headers. Good to know.