Thanks guys - it appears that at least one person has successfully wired headphones to the balanced outputs, and found the result preferable to the single-ended output. (source: http://www.pinkfishmedia.net/forum/showpost.php?p=2022722&postcount=307)
Well, I got my M-DAC today, went ahead and did some quick comparisons between the balanced and single-ended output. My (very subjective and very un-professional) impressions are (using the Senn HD600:
- Much wider soundstage when balanced (but less depth),
- better instrument separation and
- better defined/controlled, but less punchy bass.
The Volume appears to be about 10db louder (according to the M-DACs display) when compared to the single-ended output (which isn't a good thing, as it would mean that the volume has to be reduced accordingly - in this case this could negatively affect the sound quality as the volume control is a digital one).
So far, this about matches my previous experience with balanced headphones. Which means, that - in my opinion - balanced operation is, with certain headphones, in many (but not all) cases preferable. However, not all headphones respond equally well, in fact I've found that some actually sound better when running single ended.
Anyway, I'll definetly make a proper balanced cable for my HD600 and conduct some more tests. The M-DAC is great in any case.