R paing reversed

I recently bought a Grace m900 Headphone amplifier. I run the S/Pdif out of my 192 Mobile to the m900.

However, when I pan a track, it is correct in my studio monitors, but it is reversed in my headphones (and yes, I have them on correctly). I'm not sure where to find the place to reverse the pan for this stereo out.

Thanks for your help!