I have a modified ANK L5 Mentor that I built driving an active pair of ATC SCM50ASLT speakers. I use and very much like a modified ANK 4.1x DAC that I also built, so that would be my recommendation. I run fiber from a highly optimized network to a Sonore opticalRendu (high quality LPS) into a Mutec MC3+ Smart Clock USB into the 4.1x S/PDIF input. I borrowed a well broken in R26 and preferred the 4.1x in that system which should come as no surprise.
I have no experience with the other DACs mentioned.
Perhaps audition the new Weiss DAC204 when they become available as the DAC501 is my favorite, the only DAC I prefer to the 4.1x in that system.
Down the line you should audition a Puritan Audio PSM156 power conditioner which will be a nice improvement over the Richard Grey.