Plex certainly doesn’t read tags from .wav files, as there is no set standard for those tags. I’m not sure about .m4a.
Plex does read some embedded tags in .mp3 files, but there are some limitations. iTunes may store some tags in a way that Plex doesn’t like (track “1/10” instead of just “1” for example).
See this How-To for some things to troubleshoot.
