I listened to this puppy today at my local dealer and was very impressed. For the record, the picture linked above looks identical to what I heard. The dealer felt it wasn't fully broken in (had about 200 hours, and he thought 400 was optimal, which is what I've heard about digital amps) but it sounded very good, nonetheless. It was used with an Ayre cx-7 and a pair of Proac Future 5's (I'm not sure what the cabling was). I was actually there to audition the McIntosh MA6600, but the dealer felt that the ARC amp would be a better mate with my Dali MS-4 Euphonias, because he felt the MA6600 is too forward for a ribbon (which isn't exactly what I felt).
It's obviously hard to give a proper comparison, as they had different cabling, and one had a plasma between the speakers, the other had a tall AV unit.
With those caveats in mind, here's what I thought:
Sound staging was very good, left to right, but the stage was perhaps a little narrower and deeper than the McIntosh, with the same speakers (but a Mac cd player). Again, this could be because of the plasma between the speakers with the Arc setup, although I would have that that a reflective surface, such as glass, would have made the soundstage shallower, not deeper. The setup with the Macs made for a larger soundstage in height and width.
Overall the tone was very pleasant. The dealer felt it had a warmer sound than the Mac; however--and this shows you how subjective this all is--to me it sounded a bit more congested in the midrange. Bass was very competent. Highs were the most surprising, as thats what bothered me with the other Class D integrateds I've heard. Highs were free from any grain or edge, which is hard to do with a ribbon tweeter, in my experience.
Fit and finish are first rate: It's very attractive , especially the display which is also one of the clearest I've seen from across a room (plus, it's nice to be able to turn it off, or select from a range of brightness settings). Having 2 balanced inputs is great, and a rare thing for integrateds.
Listening to the same track (Bonny Rait's "The Glow"), which seems to be recorded on a slightly low level, it seemed like the Mac had a little more power, as I had to crank to the Arc up higher to get to the same level (by my judgement). It's not like I was anywhere near 100, so it doesn't really matter, and I think this has more to do with Mac's generous headroom (a conservative 200 WPC) than the Arc being under-powered. Just thought I'd note it for full disclosure.
I think this is a very appealing integrated (I'm not going to get into price, because that's relative) and, depending on what's up the chain, could easily make someone--even me--happy long term. If anyone has any specific questions, let me know and I'll write back. It's late and my memory is getting foggy anyway.