Sorry for the silence again. Calgary economy sucks at the moment, and as a job search coach, that means I'm super busy.
Still working on my review. With firmware updates every few days, the M2 user interface and other items keep developing and changing (not in a big way, but there is some flux), and that's also holding things up. Haven't noticed any changes in sound though, which - typical of the Aune products I've tried so far (B1 and X1S) - is excellent.
What I can say is I prefer the M2 Pro to the M2 standard. Hard to put a finger on why as everything is virtually identical, but there's a lustre to the M2 Pro that I didn't find with the M2. To quote what will be part of my review, "For a visual analogy, it’s like taking pictures of a pearl… If the M2 is the pearl, it’s like the M2 Pro is a pearl that’s been misted lightly to reflect more light. The pearl is the same, but in the photograph, the misted pearl has more lustre. Pro is very slightly bigger, dynamic range and instrumental clarity just a hair enhanced, but other than that everything is the same."
More to come. Have compared M2 Pro with Cayin N6, Fiio X5ii and Shaning M2 so far, and will do an A/B with the Astell & Kern AK240 and Fiio X7 later this week (both just arrived late last week).