As already stated, Nero will automatically convert MP3 to wav to store as cda on an audio disc.
If you select ISO CD in Nero, they would be stored as Mp3 files.
I believer CDex, EAC and, I think, Furio are free apps that will convert from MP3 to wav and wav to MP3. I'm not sure but Audacity may also suit your needs.
Cool Edit Pro was purchased by Adobe and renamed Adobe Audiont.
It costs $ but will do conversions and much more.
Of the above titles, Nero and Furio are burners.