as answered by PM, you shouldn't convert your sounds to MP3 and work natively in (uncompress) WAV files. You can use audacity for this.
If the sounds aren't played, they got ignored / skipped because having the wrong format. Logging via the RICE port with debug enabled would tell you additional info.
Also, compare your WAV file with a HEX editor and look for differences in the header. Some horrible tools create non standard WAVE headers which I used to skip on previous board generation. CFX provides more flexibility by parsing the header deeper and more in details, even if the chunks remain deliberately misplaced by apps like Audition.