After several hours of going back and forth, I doubt my opinion is going to change much from here on out. First, a very important proviso: I have no experience with other comparable high-end sources! So this is not intended to be a qualitative review of the Ayre DAC, but rather a straight comparison with the Duet, which I know that others here have also come to rate fairly highly in its class. I ran both through the GS-1, which apart from being an admirably neutral conduit also allows for simple switching of two inputs, and roughly volume matched each individual track with an SPL meter. Material was a selection of 24/96 needledrops and Red Book, all in ALAC format. Bit rate adjustments were made in Audio Midi Setup and were consistent for both sources. ICs and Duet breakout were identical, fine Nugget Audio products.
Anyway, the first and clearest impression going to the Ayre for me was the soundstage just blowing outward. I have never thought of the Duet as closed-in, but by comparison it surely is. Not even close. Boom! (Out-of-)head shot!
Second would be detail retrieval -- there was immediately a lot more "there" there, with both hi-resolution material and standard CDs. This threw me initially, as the Duet seemed to have punchier bass, but after listening to the same upright bass lines and kick drums over and over, I came to conclusion that what I was hearing was a more one-note response making an impression over better-delineated and more-realistic impact and decay. The Ayre seems to me to do much better with transients in general and at higher frequencies it isn't even close.
Other than that, as I said, general operation is trouble free. Truly plug and play, at least with my Mac. And of course everyone loves the new new thing so take this with the requisite big pinch of salt, but I absolutely want to own one of these. It makes the Duet sound congested and slow, and if there's a front rank of Duet fanboys I believe I've been in it! Big gear sale and ritual spousal ripping of new asshole to follow shortly. Watch this space.