In my opinion, you can burn the MP3 CD's unchanged to the disc. No advantages to change them to WAV as MP3 is a lossy format. Most probably, your CD player will not play WAV files anyway.
From the manual:The C 546BEE can play MP3/WMA formatted recordings on CD-R or CD-RW discs. You may mix any of the file types on the disc.
Cheers, eagledriver