We've seen this test before, but why not give it a go again.
I used my office computer system which consists of:
Turtle Beach Santa Cruz sound card
H/K 380i receiver
Angstrom Legato speakers

Here's the test:
http://www.klippel-listeningtest.de/lt/default.html

With the furnace clicking on and off while i was doing the test, i managed a -27dB range on average, just ahead of the distribution curve. I figure the hump at the top end of the curve is from people who have extracted the sound data and viewed a response graph of some kind to ascertain which sample had distortion and chose the correct answer. The end is too skewed otherwise.
At the bottom end the hump is likely from people who started the test, found it to be long and just clicked randomly to finish it off and see what happens at the end skewing the results downward.
Those are my thoughts on it.

Very interesting, Chess. I plugged in my Senn HD 570 into my computer and -30dB range. The distortion was extremely difficult to pick up at that point. I feared turning my headphones up past comfort levels. I don't know what sound card I have--whatever comes default in a Mac Mini.

-30db for me on my Senn HD497.

Weird thing is that if I play the whole track its hard to decern in my ears the distortion. If I only play the first 3 second of the guiter string I can easily identify it when I quickly switch A-B.
Also everytime I hear the distortion I say to myself thats how my tube amp sounds...lush and more grainy.
So in all my tests I say to myself what sounds like my tube amp and I get it right all the time up to -30db.

ps: I have a pretty high noise level on my computer fan beside me that I can still hear with my headphones on. I do not know if I would have scored higher if that sound was totally isolated.
Plus I got tinitis which doesnt help.

Whatever was after -18 (-24 I think). And I had to guess at that.

I wonder if the audiobytes will do a better job of rendering the distortion. I was listening through my laptop's speakers.

I found myself doing this, too. Much easier to discern a difference between the recordings in an immediate comparison.