Hi Rock-solid,
I am awaiting my MX2 which appears to be stuck in customs ( in the UK ).
However, I was interested in your post above as I have had a similar experience with different equipment. I purchased a Samsung Note 10.1 tab at the beginning of this year and after reading the thread on this forum about Android phones and USB dacs, I hooked it up to a Behringer UCA-202 dac. The first time I tried it, the base was very poor ( I think the general sound quality was poor but it was most noticeable in the base ). I gave up but tried it a few days later and it sounded fine ! It was OK for a few days and then I lost all the base again. I thought it may be something to do with ( digital ) volume as this cuts the bits but there was no indication on the tablet that anything was happening with the volume. I even downloaded some apps which are meant to fix volume levels etc but this had no effect - sometimes the sound was fine and at other times it was bad !
Anyway, to cut a long story a bit shorter, I came to the conclusion that I could get it to sound OK by disconnecting the dac, rebooting the tab and starting the audio software and then plugging the dac in, so as you mention above, it appears that the order it is done in, has an effect. Why this should happen, I am still puzzled about. I am surprised that you had this happen with your Mac as I have never noticed a similar effect when using PCs/laptops with dacs and I thought it may just be because using dacs with mobile ( Android ) devices is a relatively new thing.
I would be very interested to hear if you ( or anyone else ) comes to any conclusion about what exactly is happening with this issue. After all, the main point of using a dac is to extract the digital stream from the source in an unaltered state and then convert it to analogue sound. With this issue, it would appear that something is happening to the bits ( re-sampling, volume, something else ? ) before they get to the dac and I would like to know what that ' something ' is !
I shall be paying close attention to what is happening when I hook up my Audinst MX2 to the tab when I get it, but in the meantime, if anyone is disappointed with the SQ from their MX2s, I would recommend disconnecting, rebooting and hooking up in a methodical way to see if that improves the sound. I am not much of a believer in ' burn in ' but if it does have any effect, I would expect that effect to be quite small - that is not like the massive change in SQ which I experienced when connecting things in the ' right ' order.