I buy MDR - EX750 HR headphone when I plug in my xz volume go down

[Anand1977]

I buy MDR - EX750 HR headphone when I plug in my xz volume go down

[Lord_viridis]

It will, the ex-750 is meant for systems that don't already have noise cancelling, likewise, the auto optimisation won't work as the headphones go through a seperate amplifier and noise cancelling system.

That's why Sony also built High Resolution Audio Headset MDR-NC750 for Xperia models, as the system is built into the phone.