I know that I am coming late to this party, but since the ARC REF6 and 6SE are frequently bought and sold currently, I thought that I would add my 2 cents, since this is still a relevant question. After running an MSB Discrete DAC direct to my Pass Labs 250.8, which powers Wilson Audio Sabrina X’s, I demo’ed an ARC LS28SE. I felt that it was better than DAC direct, but not by much. I then got a deal on an ARC REF6 and bought it, with ARC’s stock PC. Since the ARC requires a 20 amp connector (C19), I couldn’t use my existing Audience PowerChords or Morrow Audio MAP3 PC for it. Nothing wrong with the stock PC, but I had heard how the Shunyata PCs really kick things to a different level with the ARC REF6. Having had distinct sonic improvements with my former Plinius SA100 MKIII amp when I switched to the Audience PowerChords, I knew that the PC’s could make a difference. I got a good deal on a Shunyata Alpha v1 PC, and when I installed it, there was an immediate, audible and significant improvement in every aspect of the music in my system. The soundstage was wider, deeper, and all of the instruments had a more "real" sound. Its very difficult to describe these types of improvements, because they really have to be heard, and then you will say, "ah, that’s what he was talking about." Bottom line is that if you’re spending that kind of $$ for a REF6, might as well spring for a used Shunyata PC for it! I easily got my money’s worth for it. In fact, I liked it so much, I sprung for a set of Shunyata Alpha v1 speaker cables, which kicked the whole system to another level.
I don’t want to get into the whole debate about whether PC’s do or don’t make a difference or why. It makes little sense to me how they work, but for me, in my system, the upgrade from stock was well worth it and significant. Hope that this helps!