Friends at audio store..Headphones at cost

all are respectable companies/headphones.

haven't heard Ultrasones so I can't comment on those.

Used to have Audio-Technica ATH-A900s (closed versions of the ones you listed). They were my first real hi-fi headphones, and I loved them! Super comfy, and a great all around sound that was very enjoyable to listen to. They were great for my purposes (gaming, movies, music). Bass was just right for me... punchy and fast, pretty tight too! Highs weren't too bright but they were there... and the mids were slightly recessed but I could live with it. The presentation was pretty fun and it worked great during the time I had them. Very easy to drive, and don't need an amp. They can run straight from your PC or DAP without a problem.

Friends have the DT770s, and I have a pair of Darth Beyers on the way (should be here in a week or so). Stock, they are also pretty nice. Also very comfortable, and wow are they bassy! Lots and lots of bass boom, however I found it to be not quite as tight and fast as the A900s. A tad bit muddier, but much more of it -- so if you're a basshead you'd love them, as I'm sure you've heard. Mids even more recessed than the A900s, and the highs were a bit bright and slightly fatiguing after periods of time. Didn't make my ears sweat as much as the A900s, though, and also isolate a bit better. Pretty power hungry, and require lots of juice if you want to reap the full benefits of them.
While they might not sound too appealing in my description, I still did enjoy them. They're also great all-around cans, similar to the A900s. They have more potential though, as they can be Darthed in the long run, which gives them a new lease on life, from what I've read.

The AD900s, from what I've seen posted here on Head-Fi, should be better than the A900s in that they give an airier, more natural sound to the music, without losing any bass quality or quantity, and gaining some more mids in the process.

Coming from another Radiohead fan, you have not heard Kid A until you've herd them on a pair of Ultrasones. The soundstage makes me drift away when I listen to Everything In It's Right Place.

They should be very similar. Im not 100% on this, but I think the Proline 650 is the same as the HFI-700. The Proline 750 has a more refined, bassy sound than the HFI-700, tough I haven't had much time with them outside of a meet or two. The thing that makes them all special tough is that they have something in them called "S-Logic". S-Logic is how Ultrasone makes their headphones. Instead of putting the driver straight to your ear, the drivers are offset a little bit. This gives the illusion of a much wider soundstage. I love this effect with Kid A because it separates all of the instruments and puts them in different places all around your head. You feel truly surrounded with music and sound.

ultrasone has a pretty big thread around here...i would check them out.