I've got a few thousand songs that are 320 kbps, and I'd like to downsample those to 192ish VBR to save HDD space. I know you can use the "Create an mp3 version" command in iTunes to make a downsampled version of a song, but this creates a copy (as opposed to replacing the original). What would be the fastest way to replace all of my 320 kbps songs with 192 VBR songs, including putting them on all the playlists they were originally on?