I have an Onkyo TXNR515 and for some reason, when I plug in the headphones, the speakers are not disabled. This is so frustrating and I can't work out if I'm doing something wrong, or if the amp has developed a fault. I had to disconnect everything recently so I'm wondering if I have made a mistake, however I simply cannot find anything connected incorrectly. The speakers are not plugged into zone 2 - the manual does say that zone 2 speakers are not disabled when headphones are connected. The headphones seem to work fine. As soon as they are connected to the front of the amp, the headphone indicator light illuminates and sound is heard through them. If anyone could help me I'd be hugely grateful. Thanks!