However, you cannot convert that MP3 file back to a .wav file without losing quality.
Incorrect syntax, Doug. It's not the conversion to WAV that loses quality. The quality of a decoded WAV file is the same as the MP3 it was decoded from. The additional quality loss happens if you take that WAV file and then encode it to MP3 a
second time. Each time you MP3-enocde an audio file, there is a certain amount of quality loss (however slight) since MP3 is a lossy format.
Edit: to be more clear... It's not the decoding that causes quality loss, it's the encoding.