I haven't heard anything out of this amp that sounds natural. There is very little seperation of instruments and voices. Details are glossed over and veiled. Everything has a bright sheen over it. There is no transparency to the sound. The bass control, especially the midbass is lacking.
Through this amp the Grado 60's do sound better to my ear than the HD600's. And yes, it does it sound better than the headphone output on my two channel HK amp, but for critical listening it really disappoints.
I haven't had any problems yet with channel balance.
I would like to try an amp that was voiced with the HD600's, inparticular the Shiit Asgard.
My HD600's have been sitting in storage unused for about five years since I sold an OBH10 in favor of an old 70's Pioneer amp. When the amp blew and money got tight I picked up a pair of Grado 60's. In the past five years I have really grown to love the Grado sound and their ease of drive and plug and play capability makes them a superb headphone. I swear that they keep getting better over time. But I haven't given up on the HD600's and wanted to pair them up with something decent to see if I can get that old magic back.