I sold my PWD.  It's definitely NOT because I didn't like it; it's actually a terrible story and now I really regret letting it go, especially for the price I ended up getting for it
 
I haven't owned tons of DACs like some on these boards, but I've had at least enough to tell when one is something special.  The PWD is definitely one of these DACs.  I would say this even though it wasn't the ideal source for all scenarios; when feeding my pre-amp, a power amp, or powered speakers it seemed to lose its magic.
 
The PWD by no means perfect; the screen doesn't seem all that necessary, it's probably twice the size as it needs to be (have a look inside and you'll know what I mean), the USB is not asynchronous, and the network bridge is a very expensive proposition (haven't tried it myself).  If you do some digging you may find many of our senior members here who really enjoy this source and I'm going to say that all of its praise is fully well deserved.  For me I fed it with a Halide Bridge (NOT to be confused with the PWD Bridge) asynch USB converter, it turns out the pairing was a very good combo and I'm glad I made the expensive leap of faith for both pieces.
 
In retrospect this DAC just sounds right.  It made recordings sound significantly more alive and brought forth more details than I've heard from anything else; needless to say it was a very refreshing experience to hear in my setup. Although it's a very expensive piece of gear for most in this hobby, myself included, I think I will do my damndest to get another one sometime in the near future.  The PWD is just that good.

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.