Just did a little more testing with my go-to track: Hugh Laurie's "St. James Infirmary" from Let Them Talk. All acoustic instruments and lots of them (piano, upright bass, guitar, drums, horns and who knows what else). As it's a recent fav of mine and my wife's, we've heard it on various cans (AKG Q701, K550 and Grado SR225) and a couple sets of speakers (JBLs - S38s with matching center and rears, and just in stereo driven by an old Kenwood VR-6060; cheap Polk Audio floor speakers and center with Energy rears in a much more enclosed room, again both 5 speakers and just the two floors, driven by a Yamaha RX-V467; Direct mode is best), but esp. with the Q701.
There's not a doubt in my mind that this mod jacked up the bass, giving it some serious weight, without compromising detail. For example, when the upright bass kicks in around 2m 40s, you feel it. The K550 represents it pretty well (better than the unmodded Q701), but this mod makes it awesome. There's a little guitar accent just before the rest of the band joins in, and I was a little worried it would get buried, overwhelmed, reduced in prominence somehow. Again, A/Bing with the K550, the modded Q701's representation of that guitar is still right there. Now, I'm also sure that pre-mod, that guitar would standout more, as there'd be less bass. But it's still there, as are all the other instruments. One great thing about the Q701 vs. the K550 are the subtleties it unmasks. On the Q701 I can really place Hugh's mouth in relative distance to his mic. When you'd expect emphasis on certain syllables, his vocals are closer/louder. I didn't get that same effect (at least not with the same clarity) with the K550.
Time for some more testing (iPod super shuffle of varying genres, though mostly rock, of the classic, prog and indie kind: Rush, Yes, Led Zeppelin, Neil Young (himself a genre machine!) Echo & the Bunnymen, The Flaming Lips, The Bevis Frond, Built To Spill, British Sea Power, ad infinitum). If it passes this, the mod stays for sure.
And here's a crazy idea I had whilst dreaming about modded Q701s... rather than putting the old, now less sticky, covers back, how about some plain old transparent (Scotch) tape? What about electrical tape, if it could be made to stick properly? What if I poked a pin hole (literally) in the center of said tape? The original covers are definitely not just plain ol' tape. No tape would have survived my method of removal, yet I was able to bring them back to circles.
Well, maybe someday I'll give it a try, if getting the ports covered isn't too much of a PITA.