Man, waiting for shipping sucks... But, I see someone else bought one (anyone from here?), so at least I am not alone..
That was probably me! I notice at least one more has sold since I purchased mine just after Christmas.
I'm pretty blown away by the sound quality of the M2. It has essentially replaced everything I have used up until now. I was using a DarkVoice 336SE Tube amp or Topping A30 fed by a Topping D10 Dac fed into Hifiman HE4xx for most of my listening. For portable use, I had tried the Topping NX4 portable amp + Smartphone and found it almost as good as the D10+A30 but not quite up to the DarkVoice. I also found I hated having the portable amp piggybacked to the smartphone. I reasoned that if I must have two devices anyway, I should just buy a great DAP (and one with enough power to drive whatever I might throw at it). That led me to this thread. The sound quality and authority I'm hearing from the M2 is superior to all my previously used equipment. Crazy given it's size and current price. I have since purchased the Sennheiser HD 58x Jubilee and man does it sound great with the M2.
I have used the M2 with the early firmware it shipped with, then the 2.56 firmware version and now the last 2.63 version as downloaded from the Acoustic Research web site. To my ears and using the Sennheiser HD 58x headphones, I find that the sound quality from the original AR Music Player is different than that produced from the newer AR Music Player PRO app. The original app seems to have a slightly deeper, fuller, more pronounced bass and maybe smoother, yet more lively mid range, which I prefer, when directly compared to the AR Music Player PRO app. Unfortunately, the original app is not as intuitive or easy to use as the USB Audio Player Pro based app but since I bought the M2 for ultimate sound quality, I find myself always using the older AR Music app. I don't know if this difference is simply down to default EQ sound choices made by the app developers or if its due to some technical difference in how each app utilizes the hardware.
Anyway, I want to thank everyone in this thread who let me know both how great this DAP is AND how to purchase a new one at such a reasonable price.