Thanks for this!
I see the sense in the vast majority of what you said, but can't see the truth in the cable having "nothing" to do with the difference in sound. Surely without a balanced cable it wouldn't be possible to hear the effects of a balanced signal in headphones plugged into a balanced headphone amp?!
Semantics aside, I'm very grateful for this informative post, which - along with some of the recent posts in this thread about balanced amping - has definitely contributed to me more clearly understanding how the HDVD 800 creates a difference in sound when listening with the balanced and unbalanced cables. I will likely accordingly amend any further impressions I create. Thank you.
Technically, it might be argued that there is no such thing as a "balanced" cable. Or that they are ALL "balanced". The cable has just been terminated in a fashion that it can be plugged into a specific kind of jack.
If you were to cut the plugs off of both your standard HD800 cord as well as your balanced cord you would have two "cables" that were identical. if you then compared their sonic differences either on a balanced amp or an unbalanced amp (forget the jack types, let's say you just use alligator clips to connect them to the amps), they would sound the same because the "cable" was the same. The termination of the cable is a function of the amp it is plugged into and not the cable itself. The quality of the sound differences are 100% a function of which headphone output jack you are using on the HDVD800
Your review was very useful, even more so since you actually had the same "cable" for both of the amp configuration types (i.e., balanced and unbalanced). This showed the true differences based on the amp configuration alone. If you had compared the standard HD800 cable and instead used a Headroom Fatpipe (a Cardas wire) headphone cable configured balanced, now you have two variables, cable type, and amp configuration. The review could then not be conclusive of anything. Was it better because it used the amp's balanced output, or was it better because the cable type (i.e., Sennheiser or Headroom) was different?
The issue is that there is a LOT of true cable comparisons in audio discussions. Implying that the balanced cable is somehow better than the unbalanced version when the cable itself in both cases is the same type and length of material is misleading. For example, if you were to try this same test using a Woo Audio WA22 instead (a balanced headphone amplifier) you would discover that they both sounded identical. What would that mean if you had previously concluded that one was "contributing different sonic differences" to the sound? Again, it is the amp and not the cable. The WA22 is balanced but its output is transformer coupled making each channel's output single ended, so regardless of whether you use the WA22 4 pin XLR connection or the 1/4 inch connector, the sound will be the same (and in this case the same volume as well).
One other way to view it is this: your test could have been done in a more difficult and unreasonable fashion, although it illustrates my point. You could have had a long listening session with your standard single-ended HD800 cable. You could have then just hacked off the 1/4 inch connector and then soldered on a 4 pin XLR and then did your listening from the XLR connector on the HDVD800. You would have heard the same results as you did. But in this case you used the SAME cable in both cases. The different plugs used is only a necessary function of the jacks on the HDVD800 that you were connecting to for comparison purposes.
So what you were really comparing was the sonic differences available at the HDVD800 unbalanced and balanced output jacks when using HD800 phones and stock headphone cable. You could just as easily cut off the plugs from a pair of Sennheiser cables (balanced or unbalanced or both, it doesn't matter) and then opened the HDVD800 and Soldered the identical headphone cables directly to the backs of the jacks. Your results would have been identical. Unsolder from the jacks and swap the cables and resolder. Results would be the same. the Balanced output produces better sound regardless of which Sennheiser cable was soldered to it.
I hope that none of this sounds condescending at all (it sure ain't meant to be). I think part of the issue is that we have to spend >$200 and wait forever to get a stock cord so that we can use our phones on the HDVD800 the way it was intended, so the improvement in sound appears to be all about this cable that we have to acquire. When we plug that great expensive cable in and get far better sound than we had, we tend to think it's the cable. This is the kind of mis-direction in audio that can confuse things.