Do you want this, probably?
(
~pathBase = "C:/folder" // ~pathBase = "sounds".resolveRelative;
~subfoldersOfpathBase = PathName(~pathBase).folders;
~allSoundFiles = ~subfoldersOfpathBase.collect{ |aPathNameInstance| SoundFile.collect(aPathNameInstance.fullPath +/+ "*") }.flat;
~path_allSoundFiles = ~allSoundFiles.collect{ |aSoundFileInstance| aSoundFileInstance.path};
Post <<< ~path_allSoundFiles
)