Problems tagging .aiff files

I have a few .aiff (lossless) files that were exported from a program called 'ScreenFlow', some of you may have heard of it. From what I've heard this file format does not support meta-tagging - For example album artwork.

While the artwork tab in the Info dialog (The one you get to by hitting Cmd+I after highlighting any song in an iTunes playlist) is selectable and does show up if I put some in, after closing the dialog nothing will change. However, the song can be renamed and take metadata like Artist, Album Artist, Genre etc. I think this is because none of this actually effects the source file, just how it shows up. For some reason album artwork is different.

So that's my problem - Let me also note that iTunes is not sourcing from aliases, I have full read-write capabilities on each file and the pictures I am attempting to load are pretty much universally recognized - .png and .jpeg. Simply changing the file extension voids compatibility between iTunes and the file (Will not open, which is pretty much what happens all the time when you change file exensions, anyway). I was hoping someone could point me towards a compressing solution that could turn my .aiffs into a lossy format like .m4a, or anything else that supports artwork.

I am running Mac OS X 10.6.8 and iTunes 10.6.3.