Weile waiting for my ATC SCM11s loudspeakers (the dealer will contact ATC factory to geht an estimate about the delivery), I'm listening with my headphones. I used to listen to the GSX Mk2 with my preferred headphones, the Sennheiser HD800. Just out of curiosity, I switched the amp to single ended and connected my long forgotten Grado GH1 on (large cushions on). I was amazed how well they pair with the GSX amp. Very revealing and transparent headphones. Particularly with the record I'm streaming through my Aurender (Foehn Trio, 'Call of the Mountains'), the GH1 produce a very intimate and pleasant sound. It's good to switch headphones from time to time!