My ARC DS450, is a very capable and musical amplifier. I know Arc uses some proprietary parts in it, and has an analogue power supply I believe, or something to that effect, which doesn't make it like many of the other class D amps discussed. All I can say is, that is a shame that many bad mouth this topology.
I will say that it did need a massive break in period. At first, I will admit, it was murky with little air and honestly didn't compare to my hd220, but now I don't miss it at all. Would I like ref 150? Yep, but I think a ref pre to upgrade my LS-17 would be a better upgrade. The DS 450 is an effortless poweramp, that had more than enough resolution, warmth and musicality to get your foot tapping of hairs standing, depending on what you want at that moment.