Great! Please make sure to add a preamp option specific to Opus though, since its replaygain implementation use a reference level of 84 dB, 5 dB lower than normal Replaygain. It would be nice to be able to match volumes between Opus and other codecs. Edit: on second thought, it might be simpler to systematically adjust Opus reference level (84 dB) to Replaygain reference level (89 dB). If users prefer the 84 dB reference level, they can always use the preamp.