Having had the HF-2's on hand for a couple of weeks and having had the opportunity over the last few days to get in a lot of listening, I think I'm ready now to start posting about them, though I will post formal impressions in the next week or so.
To me, I feel they are refined 325i's (the previous i's not the ones with the new cable). I think that the driver used is very close to the 325i's where the sound literally jumps off the driver. I think I read Aaron (immtbiker) felt that they were as hard hitting as HP-1000's with excellent, powerful bass and mids. I concur with this. Where I always felt the 325i's fell short was in how upfront the sound was and how the highs sounded after an extended listen. The 325i's helped over the 325's but next to the RS-1's or PS-1's at the time, I would always go for those over the 325i's despite them being more dynamic to my ears.
The HF-2's retain the dynamic punch of the 325i's but with better highs and a richer and more linear sound. These headphones are dryer than my vintage RS-1's, PS'1s or PS-1000's but they are more liquid than the 325i's that I remember.
I'll have a chance to directly compare in a couple of weeks when Beagle and I get together and I get a chance to listen to his 325i's as well as the 200's for comparison.
In terms of headspace, the HF-2's have a big soundstage but a narrower headstage where the music is still very up close and personal, yet the notes can trail off into the distance with easily audible effect.
For me, comparing as I have against the PS-1's and PS-1000's, I don't know that I would call the HF-2's baby one or the other. I would rather say they are nearly perfected 325i. The HF-2's don't have the space the larger cupped Grados possess. They aren't as liquid sounding as the very retro RS-1's, PS-1's or PS-1000's but are more liquid than current RS-1's and GS-1000's (no idea on GS-1000i's).
They are very fast phones too but the bass isn't anaemic by any standards which seems to be the tendency with responsive headphones that are defined as fast (Etys, Qualia, Stax).
The most defining sound for me is the unreal palpable snap to the notes, particularly bass and mid to lower midrange. The sound is so lively and jumps right at you but in a non-exaggerated way. By that I mean it doesn't sound fake. This to me is very reminiscent of high efficiency horns, where the dynamics are a distinguishing factor and one where many a listener becomes so addicted they won't settle for any other type of speaker.
After re-reading your comments, I find that your review is easily the most naturally intuitive and consistent of those I've read to this point. I think my hope had been that the HF-2 would be most comparable to either the RS-1 or PS-1. Therefore, when you mentioned the 325i, I was left with an overall perception that the quality level of the HF-2 was competing at a lower level of refinement than I have been hoping.
However, it seems that it's a more complicated picture than my initial assumptions would have led me to believe. The way you describe it, it almost sounds as though the HF-2 succeeds at blending the relative strengths of both the Grado woodies and the aluminum chambered housings.
The bass weight and mid-range seems like it has characteristics I more closely associate with the wood chambered Grados. Yet the speed of attack suggests that the bass retains the metal characteristic...or at least the speed that I associate with the 325i's. It's easy for me to forget that the 325's actually do a lot of things well.
I'm still a little unclear about the difference in the quality of the highs between the two phones. I am very relieved to hear that they're not as bright as the 325i's, but that doesn't necessarily say anything about their relative quality. Are they as extended as RS-1 highs? Etc...
Also, the soundstage issue is still something I'm unclear on. I've read some people mention that they believe the soundstage is a product of a recessed mid-range (in comparison to other Grado's). I've got high hopes here, but am a little nervous that I'm setting myself up to be disappointed. I'm hoping they're more like RS-1's than what I associate with the lower end Grado's.