I've heard this before and it puzzles me, but I guess it could be a preference thing. I used to own a pair of HF-1's, and I liked them well enough, but I thought the RS-1 was a clear step up with the right amp. Recently I've been falling back into the Grado camp, and flirting with the RS-1 and MS-Pro. Maybe I should give the HF-1's another listen given my new tastes.
Also, though I know there must be some variance in Larry's mods, I thought that the HHF-1's I heard [pixel_pusher's pair] were actually worse than my stock HF-1's back when I owned them.