I'm having a similar issue with my V 60. Plugging the headphones in would mute the speaker, removing them would un-mute. But after a couple weeks of use, unplugging the headphones would no longer un-mute the speakers. My workaround was to switch to 'Line' mode to use the amp without the headphones. Tried a firmware update, factory reset, nothing seems to work - if headphones aren't plugged in, no sound from the speakers unless I switch the Phones mode to 'Line'.