I had the MKV and liked it very much. I use my computer into an OMZ dac as a source. Upgrade got to me and I went for the GS-1. I listen through an RS-1 and K701.
The difference is substantial. The MKV is nice, particularly for the money, but the GS-1 is better in everyway. It has more balance and neutrality, which is what I value in an amp. The source and phones should have the signature. Detail, seperation and tonality are all part of the improvement plus the GS-1 is dead quiet. Very black background.
I sold the MKV after I got the GS-1 (with stepped attenuator, btw). The price difference is quite large, 3x as much. I am always amazed with the sound I have now, so it was worth it for me.
Hope that helps a little