From my extended listening of a friend's pair, the Ed 8 is a sonic superior, although not by much. The Thunderpants have this smoother, creamier, more polite nature compared to the slightly more brittle temper of the Ed 8s. This is really evident in the bass and treble presentation.
While the Thunderpants have a smooth, even, warm bass, the Ed 8 comes out with a more forceful, slightly (just slightly) more grainy bass. Not grainy as in low-def, but with more texture, grit and kick.
For the treble, as Jude mentioned, the Thunderpants eschew the fine details for the smoother ride -- for example, violins sound lush and clear. On the other hand, the Ed 8 bring out the more agressive nature of the bowing strokes. The 8s bring bring out the subtle overtones slightly better; while the detail is there on the Thunderpants, one has to look a lot harder.
Both are VERY musical with great soundstaging, just different flavors.
I'd describe the Thunderpants as high-mid-end while the Ed 8s are low-hi-end. Just for reference, the LCD2/HE6 would count has mid-high-end in that system.
The Thunderpants are an excellent value, compared to the Ed 8. But IMO, not its sonic (or functional) superior. I struggle to call the Thunderpants true "high-end" because of the diffused treble, while the Ed 8s perform admirably there too.
Btw, can someone answer my question about the Ed 8 bag please?

thanks
JB