I do not know.I figured that none doesn't mean anything to VLC. It tries to open it anyway. Does the audio configuration option in Directshow tab offer any audio options for your audio device?
It's Your say about command string too?Because if VLC is associated to autorun .m3u files from internet browser, you could use evil m3u files to do evil things. Only #EXTVLCOPT parts are barred.
Sound not usable in "dshow://" with empty. Video is normal.Does the sound work if you leave dshow-vdev empty?