batch processing files in nested folders

i want to convert an old itunes library of files from mp3 to wav.  Was hoping i could just drag the root folder onto audition's batch process window and have it drill down and recognize the files.  It doesn't.  Instead it seems i can only add FILES, not folders.  NCH Switch does this, but I don't want to have to pay $25, since I already have Audition.

Any ideas? Am I missing something?

-bewildered in bedstuy