AV receiver that can switch between speakers and headphone amp?

I have been seeing those Sennheiser HD600 and HD650 headphones go on sale all the time lately. I want them badly, but I want to be able to use them on my AV receiver with proper headphone amps.

I hear the best way to connect headphone amps to a receiver is through the pre-out ports. Unfortunately, I read in my receiver's manual (Yamaha RX-V765) to not connect things to both a speaker outputs (I have 3 speakers connected plus a subwoofer to the sub out) and the pre-outs at the same time. I also looked into connecting to the receiver's zone 2 or AV out, and the receiver manual says those only work with analog audio sources.

Are there any AV receivers out there that are more accommodating to headphone amps? Or is there a way to work around this? Thanks.