Rawhit
By chance, I think I can answer that. I have used SET's for years and the 20watt Ayon Spark is my backup amp at the moment. I like it a lot, clearly and perhaps suprisingly, better, in my view, than the Viva Solista I had several years ago.
It is perhaps unfair to compare it with a power amp twice it's price, but it is clearly softer, less dynamic, with a definite loss of detail and imaging. It is a typical tube sound, very slightly warm and lacking dynamics. The ARC retains the organic tube sound, but is markedly better in imaging, detail, base, dynamics, both macro and micro. I would say soundstage depth, which I value, is about the same. The ARC for me, is hard to fault, maybe soundstage width could be better, but depth matters more to me.
Comparing with a good SS amp and Lou, the Daedalus designer, likes Modwright, I'm afraid I just don't get it. I find even good SS, which the Modwright is, grainy and unmusical. It sounds like recorded music, not music, but that's just my view and priority