"But I don't use Audacity to convert this to mp3 - I add the file to my iTunes library and then convert to mp3 - which keeps sound quality and creates a file roughly 1/10th of the .WAV file size."

If you end up with 1/10 the size you are making a 128k MP3, which is OK quality but on good speakers you can tell it's not the original. Which way you do it (Audacity or iTunes) doesn't matter much if you produce the same bitrate MP3.

I know some converters are better than others, but we are talking very subtle differences here. Audacity uses LAME which is a good encoder and used by may other programs, and there's some evidence that iTunes's MP3 encoder isn't the best.