After listeing to these things for about a week, I think I've had enough time to form an opinion and well - I'm bemused by these things. They're really source sensitive at 100ohms. Through my Asus Xonar D2 soundcard they're pretty much as iancraig10 described. The bass is overly strong and boomy, with the mid and treble sounding recessed. It just sounds wrong like this, as if I'm wearing the headphones over a wooly hat.
I tried them with a Hitachi DA.P440 personal CD player and it's completely different to the Xonar. There's nothing like as much of a change. There is a difference but it's almost imperceptible. They do still sound better with noise reduction on but with it off the boominess isn't there but the overall sound still sounds a little 'shrouded'. At 330 ohms they could be mistaken for my DR100s (sound is less open and only slightly more detailed).
Back to the Xonar at 330 ohms. They sound like a completely different set of headphones from 100 ohms. The sound is natural in tone and detailed. The detail increase is immediately obvious when coming from the DR100s. Everything is immedtiately more enjoyable. Listening to classical music, I can hear the solo flautist take her breaths, the keys being pressed and the pages being turned much more clearly. Rock is more natural sounding, clearer, with excellent separation between the instruments. Drums are so much punchier you can pretty much feel it. One of my standard headphone listening tests is Van Halen's 'Hot For Teacher' drum intro and I found myself thrashing about like an idiot with the NS-1000s rather than moving on to the next thing like I normally would. Electric guitars have a real sense of attack. I've not heard any Grados but I would imagine that's what they sound like.
I'm assuming the LM4562 OpAmps in my Xonar are much better at driving high impedance headphones than whatever is in my fairly cheap CD player. With noise reduction on with the Xonar these things sound lovely. With it off they're a mess. Both modes sound pretty good though the CD player, with the noise reduction mode sounding marginally better. Bought myself a bunch of rechargable AAAs yesterday as I think I'm going to get through a lot of them. Without noise reduction, I think I may have found a set of headphones that sound better unamped!
I tried the Dolby Headphone mode on the Xonar as well as the Hi-Fi mode. It throws a pretty good 'fake' soundstage, making up for the closed design. This is the second set of headphones I've tried where I felt that the Xonar's Dolby Headphone didn't sound 'artificial'. The other was the HD600.
A word on that hiss with noise reduction. It's definitely there, unfortunately, and it's pretty noticeable on quiet tracks. It's a bit like very quiet pink noise. By chance I put my hands on the sides of the headphones and it shut up - so I'm pretty sure it comes from playing out of phase sound to you picking up. I wonder if it would stop in a truly silent environment? The noise reduction seems to work well. It shuts up the fan noise from my computer, which is a big bonus.
Anyway - I intend to try a bit of gaming and movie watching, as well as listen to some more music. Fort the price I paid I'm very happy. If I'd paid full RRP, I think I'd find the hiss a bit more of an issue.
Anyway - Here's a rundown of the music I've been using to test these things - all CDs.
The Celtic Connection (Bunch of stuff like Clannad, Maire Brennan etc)
U2 - The Joshua Tree
Classic FM - All time great wind chamber music
Nick Cave and the Bad Seeds - Dig Lazarus Dig!!!
Van Halen - Best of Both Worlds
Nick Harper - Seed
Scott Matthews -Passing Stranger
Jon Gomm - Hypertension (bit like Michael Hedges with more singing)
Led Zeppelin IV
Diana Krall -Love Scenes
Queen - Greatest Hits 1, 2 and 3
Essenchill (Nitin Sawhney remixes of variety of music)
Nitin Sawhney - Displacing the Priest
Ryan Shaw - This is Ryan Shaw
Evanescence - Fallen
The Story of Acid Jazz
Nine Inch Nails - Pretty Hate Machine