Nitelife

Of course headphone volume is controlled by main volume which you know
To get it even louder you must increase volume of Audya Soundcard
But this of course will raise the overall volume output of both the headphones AND the mains

Here's how: (from AJ on old post)

Press MENU
Press KEYBOARD CONTROL (F4)
Press PITCH/VOL/TRAN (F1)
Press SOUND CARD LEVEL (F2) and increase or/and RIGHT BOOST (F6) to increase the boost level of the right when you press RIGHT BOOST (from the default screen U5/10)

I really wish headphone volume could be independent from main
Or at least be able to be programmable onto one of the Audya sliders so we could have independent control.
In a live situation that would often be very useful