Main reason was for using a 13meter balanced cable (sometimes) to sit in a different room.
Using the 13m cable SQ is not so good - i did believe that using a balanced cable, there will not be any difference by using 3 or 16 meters.
Few people reported it was the case but after switching firmware numerous times I couldn't convince myself they sounded any different so settled with the latest one as it fixes few issues -including random crackles in the left channel- and add functionalities.
The "clear" superiority of v.90 is a bit of a self-perpetuating myth that once started kept going, not the least because of technical issues, it could not be retro-fitted with all the other improvements, and as most audiophiles know: that which you cannot have must the best I doubt many could pick out a randomly installed firmware version as clearly as they claim... we'll never know though, and of course that is a discussion better left elsewhere.
More seriously, since there is no constraint in switching firmware version forward OR backwards, there is no harm for you in trying and hearing for yourself! Ultimately, after all it's your ears listening. Try switching filters and honestly ask yourself if you can -consistently- hear the difference (for me it's only barely between Optimal Transients and Optimal Spectrum, but not even remotely between OT XD or OT DD for example) In A08, the Phase Invert also switches between some DAC methodology that is supposed to alter the sound signature (like A05 vs A06) but I cannot hear a difference for the life of me. Try it yourself!
If you can't, then there is no need to worry about an audiomaginary (tm) loss of sound quality when switching to a newer firmware version which has real benefits like less bugs and nice features like screen dimming and much more...
Also, apparently John W and his longtime coder Dominic have started work on a "super v90" that combines the SQ of v90 with all the other benefits of the later versions.... and I can already predict that some people on PFM will complain that they can still hear a difference, and of course it won't be as good as their mythical v90...
In case you try various version without wading through 100s of PFM posts: v.99, the first version to include a reliable fix for the left channel bug, is considered by many to be pretty bad sounding otherwise. And all the Axx versions were incremental improvements, so I'd just go with the latest (A08).
Useful link: M-DAC Wikkii
And most importantly, don't forget to enjoy your music on this really nice DAC/HP amp!
I had an adapter made to use with my balanced headphones straight out of the balanced out. Unsurpisingly, the HE-6 distorded horribly, but my JVC DX1000 and H700 sounded quite good but I am not sure it was any better than the HO so stopped using that way. However, 600 Ohms might benefit more so it is worth trying.
Hmmm... how much deviation from the actual sampling rate over coax would you say is acceptable before you should start thinking about getting another source (sound card in this case)? I'm seeing values like 176.407 or 192.003 kHz for example. I don't know, maybe I'm just nitpicking.
I'm a very recent M-DAC owner and haven't really been following the massive threads at PFM and so on, so this question might have been asked to death already, in which case I apologise.
I recommend you change the setting in the MDAC to nominal frequency as to stop yourself becoming paranoid
Those readings are excellent by the way, that's if the MDAC measurements are that accurate, within ~0.001 %, but somehow I doubt it.
Out of sight, out of mind...
Got this dac yesterday, amazing
Not burnt in yet, but initial impression are.
A0.8 is darker and more narrow.
.96 is a tad brighter
.99 is brighter still with emphasis on highs
.90 (stock) is the best to my ears.