Pros: "Neutrality", non-fatiguing, extreme details, hefty build quality
Cons: Fit for small heads is terrible, weight, not for bass lovers, high price premiums, poor lettering, low supply :)
Rigg: FLAC, Stello DA100 Signature (optical), RSA Raptor
It's a bit scattered but here are my notes on the HP-2:
Bass kick is there but doesn't carry weight emphasis (Listen to Chemical Brothers ~ music: Response), quantified in between the hd600 and hd650, would venture to say the bass sensitivity of hd800 (aka 0% bloat) is lower and fuller. "Punchy" but not for bass lovers.
Details: in this tier of headphone detail retrieval leaves nothing to be desired, you can hear every bit of everything.
Nowhere near the speed of hd800, I know that the hp-2 is no slouch but it almost sounds congested going from hd800 to hp-2, then I realize it's just slower and more relaxed. Reminds me of Led Zeppelin's artistic style; not razor sharp in accuracy but damn good in its own right.
The Rs-1i is much more fun, Hp-2 is extremely neutral across frequency range, coloration might be a tiny bit on the high end. This phone is very much alive, have yet to hear anything that sounds "artificial". As a result, you would probably be able to listen to these for hours without listener fatigue; comfort on the other hand depends if you can get a good fit.
Songs that I would know like the back of my hand, focus sometimes sound drastically different. Shiny toy guns ~ I owe you a love song (btw I miss the old lead female singer): can hear female singer's voice tire/breathing. Metallica ~ blackened, Tool ~ Lateralus: Songs where the drum or bass were once front and center now sound second to everything else. On the other hand songs that have piercing highs are a little easier on the ears.
Songs with strong symbols and kick drums sound metallic/microphonic, bouncing around inside my skull. Maybe this is just the amp?
Has greater soundstage than RS-1 but still in the realm of Grado. To be honest, even though I own the hd800 and CD3000 most of the time when I listen to music I'm not listening for the SS.
Hp-2 vs. any other grado, they are night and day different; none of the "slight differences" like most of the lower models.
Love them, but wouldn't want to listen to them exclusively. When you are this neutral, sometimes you want more coloration.
Favorite genre with the HP-2: probably blues. IMO the hp-2's are very listenable with poorer quality recordings, ie. the Doors; unlike the other Grado's I've heard these are very polite.
Build: Beautiful; these make most modern mass produced headphones look like children's toys. Apparently the red printed lettering is SUPER fragile; I am scared to touch/rub around the cups!
Headband is probably made of steel or comparable, have fun trying to bend it. My head is smaller so to bend the headband of a rare/expensive piece is rather nerve racking.
Cable quality is supposedly legendary, in terms of thickness it's solid but lightweight compared to today's "i" grados with thick cables. Also the Y split isn't sloppy!
Screws keep the "settings" of the rods, but I think I will avoid using them to prevent leaving marks on the rods from abrasion. The cups are quite heavy and as a result the rods tend to slide down on the blocks on their own.
IMO you don't want these to sit loosely on your head, since the flat pads bring the driver so close to your ears and the weight will have them sliding around, you need a relatively snug/stable fit.