I have a desperate need to connect two headphones to our Audya.

However, when I set the parameter : Headphones to out 3 & 4 to "on", I loose my regular headphone out channel, but there's nothing on output 3 or 4 when I connect my headphone to it.

T..he 3&4 out is two mono jack, and not a Stereo Out that need a Headphones out...

I think it is happens because need to be routed the Outputs from MENU/OUTPUT ASSIGN/OUT 3&4. By using the CURSOR buttons you can select the source one by one, and set the output destination, choosing from Main Stereo or Main + 3&4.

I would also recommend a headphone amplifier. Ketron have erred on the side of caution and disabled the ability to turn the headphones up beyond a safe level - fine for home, but no good for live monitoring during a performance. I have spoken to them about this but they insist the levels are set at a safe point and I guess they do not like the idea of someone claiming damages.