CD ripping

flac 0 through flac 8 (I think that is the highest) are lossless, compressed formats. dBpoweramp also provides Uncompressed flac, which is not compressed at all. It is basically a wav file with a flac header. If anyone is concerned about flac compression, uncompressed flac is a good option since it has the metadata capability that wav lacks. There are versions of wav with metadata, but they seem to be pretty nonstandard. I think most players play uncompressed flac.

If the m4a files are lossless, then I would suggest converting a couple to uncompressed flac, flac 5, wav or one of the Apple formats and comparing them to see if you hear a difference. Then re-rip the same album to your preferred format and see if you hear a difference. It is easier to do the experiment than to re-rip everything. You can also re-rip at a later time.

If your m4a are lossy, then definitely consider re-ripping.

Obviously, take your time upfront, before launching a time consuming process.

Most people who can hear the difference in formats, knowingly or unknowingly, have bats for ancestors. Happens mostly for people with ancestors from Eastern Europe, around Transylvanian :)

Sounds like you have some work ahead of you, but in the end the music will be improved. Sunday football season is coming up. I find that a good time to do  mindless tasks.

Not a Mac guy, but I would assume all you need is an external CD/DVD drive, probably connected with USB. Your player may have the ripping software or you can get dBpoweramp or some other ripping software.