I was looking at an integrated amplifier from Yamaha...the A-960!!....and it has a button, in the middle of the front panel that is label "main direct'. One push turns it on (and the button lights up) push it again, and it goes off. But what does it do? Is it switching between the two states of 'main' and 'direct'? What does that even mean? Some amps switch between two sets of speakers by calling them "main' and 'remote'--but this one has regular "A" and "B" buttons to do that. Can anyone tell me what this button is for? I asked the guy who was selling the amp--and he didn't know!