I had to look up those headphones. They have a 5.1 analog connection, which I assume you're hooking up to the receiver's pre-amp outputs. Unfortunately, the Model 1050 (like pretty much all receivers) feeds the exact same signal to those pre-amps connections and the internal amplifiers, so there's not much you can do at the receiver. If you had a separate power amplifier, you could shut the amp off, but that means buying a separate power amp. Even something like the Model 7075 is going to run you $700.

A somewhat clumsy work-around would be to add either a five-channel speaker selector or multiple stereo speaker selectors between the receiver and the speakers, at which point you could switch the speaker selector(s) to an unused input and shut them down whenever you are using the headphones.