I was at the NY Area meet this weekend, and I tried out both the HP1 and HP2 for the first time. I can't even recall the source of either, and of course, a meet is not the absolute best listening environment, but believe it or not, I thought both the HP1 and HP2 were fairly close in sound to my PS1000, with the edge (between the HP1 and HP2) going to the HP1 - I really liked the polarity switch on them. That said, to be honest, and this might sound weird, but I would say my PS1000 sounded more like the HPs than the GS1000i. Of course, Zanth has tons more experience than I with the HPs, so maybe it's just another case of different strokes (or ears) for different folks
Interestingly, after letting my GS1000i's sit around for a couple of months while playing with my PS1000 and my HD800, I tried 'em out again yesterday, not on my main rig (the Cary Xciter amp/DAC combination), but on my Headroom ultra micro stack, expecting the dreaded "sucked out" mids, having somehow convinced myself, no doubt by reading too much, of this - and lo and behold, listening to the Allman Brothers, some Bob Marley, and some Mozart piano sonatas, I have to say, the GS1000i's were absolutely great - the soundstage is just amazing - perhaps a bit larger than the PS1000 (the PS1000, in turn, has a larger soundstage than the HP1 and HP2s I heard the other day). While I didn't do an A/B with the PS1000 on my Cary Xciter rig (which was voiced for the GS1000), I would say - and this could well have to do with the Headroom stack I was listening to with the GS1000i's - that the GS1000i was slightly less crisp than the PS1000 with respect to percussion (less snap and zing), and was perhaps, overall, a bit brighter than the PS1000 - but not annoyingly so at all. My little listening session the other day reminded me why I bought the GS1000i in the first place - I think they're excellent cans, even if the PS1000 (at almost double the price) are sharper, more resolving, and a bit less "congested" sounding (again - this does not mean the GS1000i sounds congested - just when doing a hyper-technical analysis and comparison to the PS1000 on a different rig).
In short, I think the GS1000i has been sadly underrated by many, even though the price, of course, ain't cheap, and the Grado quality control issues still lurk out there. Knock wood, mine look and are holding up nicely....