I'd be very interested to see how the M51 compares to my 20 year old Micromega. The two other (modern) DACs I have are no better overall in my current place, although they have different strengths and weaknesses. I can't really draw any conclusions though due to my mains power varying so much. I tried an Arcam D33, which I really liked, but it may just have been a good couple of days... I'd also be interested in comparing the JKSPDIF with my Hiface EVO. I tried the battery pack for the EVO which made a big difference, but I couldn't be bothered with the hassle of 'is it charged, or is it on mains?' that comes with it. I've discovered that the EVO is very sensitive to power quality, so battery beats my current mains, but does it beat decent mains? That I don't know.
I spoke to my local dealer and the "hygienic demos" they offer are just antiseptic wipes, not what i thought they meant, so I've ordered some replacement earpads for my HD800s as they're going to need them soon anyway. I also ordered some replacement pads for my old HD650s and will bring them along as well, along with some Grado SR-80s. And I wonder where all my money goes.