Wav will not put back what compression (Mp3) took away. I can't really see how it could sound better. Have you tried lossless, ie Flac?
Quality of MP3 to .WAV Conversion
I belatedly discovered some of the sharware and free programs that convert MP3 to WAV formats. I've played around only a bit and the MP3's do expand enormously into WAV format. The WAV files seem to sound a bit better than the MP3, but it's not a big difference. Is is possible to generalize about the quality of such converted files? (So far I'm not a fan of MP3 format sound.)