Man, I have been so busy, but I finally have an update:
Thanks to Triggerfish, I now have a stock ES10 to play with.
Having extensively tested them over the past week, the house sound of the stock headphone wasn't destroyed, fortunately. What's different? My pair has a less aggressive sound, and it's smoother overall. Soundstage is clearer and cleaner, and also wider. The stock ES10 seems to congest at lower frequencies, but my pair doesn't do that. Treble extension is better with my pair, while the stock ES10 seems to top out around 9-10KHz. Also, stock ES10 is just a tad sibilant with certain songs, and that's especially noticeable with the ESW9 ear pads. My pair presents a smoother treble range, but it's still cleaner and clearer overall. Best of all... both pairs have bass that hit just as hard, but my pair extends far deeper into the sub-bass region, with better bass details and clarity all the way down there, so instead of overpowering congested bass, it's more atmospheric. These differences are even more pronounced with the stock ear pads, or with the ESW11 ear pads. Stock ear pads sound smoother up top for the stock ES10, but then soundstage suffers tremendously. ESW11 ear pads make the stock sound even darker (whoa!), and even more congested although midrange is slightly cleaner. My pair with ESW11 is tremendously more spacious than stock pair with ESW11 ear pads, and still wider than stock with ESW9 ear pads.
So to summarize: it's the same sound as the stock ES10, just with more clarity, more space, slightly more smoothness and better separated bass.
But that's a few days ago. I'll post instructions on how to perform this mod tomorrow. Just gotta organize my notes. That stock ES10 headphone has been modded, and I'll lightly sand the ear cups before shipping it back to the original owner on Monday.
Thanks again, Triggerfish! I think you'll enjoy the headphone very much when it gets back!