I haven’t had any luck looking for a FLAC ACM codec. Can anyone point me to it, or to a good lossless alternative?
I did a search, but couldn’t find any lossless ACM codecs. I don’t think there is one (based on what I read on some forum threads shown in the search results). If it’s for archiving purposes, I guess it’s better to either leave the audio uncompressed or keep it losslessly compressed in a separate file. If not, use something like Ogg Vorbis ACM with a high quality (q5-10) setting.
You could always try WinRAR. Just out of curiosity, what is wrong with FLAC?