Any distortion at 12:00 is not coming from your Woo using low imp, maybe tubes or DAC/source player. Check out the gain from your source player/DAC. I have had my Woo at 2:00 and still no distortion.
That said I did hear a little distortion in the lows and highs when I first got my HE6's. After about 80 hours on my HE6s I found the distortion was coming from my Realiser when I went below a gain of -15 but I have corrected that with the addition of my ADG19 DSPv5 and not loosing any AQ. Now I can use my Realiser at gain of 0 with NP, there by lowering the volume level of my Woo. I should add that the distortion was not there with music but only with movies.
Anyway I now only use my HE6's.
I emailed Jack to tell him about my experinece with the WA5-LE and the HE-6 reagrding the difference in sound between the high impedance and low impedance outputs. Here is his reply:
"There is no problem at all using the hi-z output. I am having the same problem here. This is puzzling us as we cannot get the reason for it. I will have to talk to Fang at Head-Direct to see what makes this phone different.
At least I can run the HE-6 out of the high impedance output safely where they sound magnificent.