OK, I'll take a stab at this. We only had the 3.1x Balanced for 3 (very looong) days and have had the 4.1x Balanced for two months or so. Have not heard the 2.1x balanced. We have tried them with both the Accustic Arts transport as well as the Audio Note CDT-2.
The CDT-2/3.1x balanced is roughly on par with the Audio Aero Capitole (though the Capitole with the Accustic Arts transport is more better). On well recorded CDs - the Audio Note has more detail, separation, and a quieter background. On badly recorded CDs (a category in which I include a significant percentage of all CDs - well, we started collecting CDs in the early 80s, YMMV), the Audio Note was sometimes not quite as much fun to listen to as the very musical Capitole.
The CDT-2/4.1x balanced is in another class altogether. For one, it sounds excellent with all grades of CDs. For example, we played an early 80s recording of the Birds, the original of which is pretty terrible and the CD recording just made it worse. It sounded pretty darned terrible on the Accustic Arts, Chord64 DAC combo (which in general is not so bad, having just the slightest touch of the digititus). And it was actually quite good, musical and really enjoyable on the DAC 4.1x B. No second harmonic distortion was added to make it sound passable - it was clean and detailed .. the way it *should* sound.
The CDT-2/4.1x just sounds... it sounds like nothing. It does not sound like analog (not sure redbook CDs have the dynamics to sound like Analog), it does not sound like CD, its sound is almost invisible. At least for me, when I try to listen hard 'at the sound' I find myself listening 'to the music'. I will probably learn to detect flaws in the sound - certainly can in all the other digital out there that I've heard for more than a few minutes - and you probably will too. But this is good enough that whatever flaws may exist are just small enough that maybe, just maybe, they will be revealed as instrinsic to the redbook format and just something we will have to live with (like pops and scatches on vinyl).
You ask for specific differences? Whereas the 3.1x B has no digititus (aka harsh pokes at the ears with an ice pick), great detail, pacing, separation, and is an amazingly solid performer - the 4.1x B has an integrity, and coherence that makes the music seem to come from the same cloth. Notes flow more naturally, not with the more realistic dynamics of analog, but not with the abrupt start and stop of digital either. The range of tones also seems much more detailed - how to describe this... the variations of the tones within notes seems much more smooth, like there is more detail, but not. It is like using a very small brush to paint a simple painting - lots of very tiny variations in the color, but not a lot of extraneous unnatural highlighting of details.
Well, hope that helps!
-Mike (dealer for everything mentioned except the Chord64 DAC).
