I also just purchased used Rossini Player. Each jump in output voltage setting adds about 10 db. So if you happened to be at .6v and playing pretty loud already and you accidentally or naively selected 6v in the Mosaic app you could immediately increase volume by 20 db (30 db if you were on .2v) and this really is not ideal, and potentially unsafe to hearing and equipment. Given that changing output volume is not a frequent adjustment, it seems to me that when this selection is made the app should automatically reduce volume by at least the amount of increase that will be created, allowing you to then bring the volume up to the new desired level.