Running an SC-61 Pioneer AVR and purchased some Sennheiser RS180 headphones. I've never run cans before on this AVR. When I plug in via the headphone jack, it goes from whatever mode I'm in to stereo and they work fine. Problem is, all my speakers shut down but the mains, they won't go off. Tried an old set of headphones, same thing. Checked my speaker settings, but I must be missing something (probably simple), just can't figure out what...any thoughts?