I have the MDR-1R and tried the NAD HP50 recently... the NAD weren't all that comfortable on me, but seems better than the Focal Spirit Pro/Classic. 1R are super comfy plus feels more like portable phones.
sound-wise, NAD wins by quite a bit in terms of just overall sound quality. I have modded my 1R and prefer them to stock, taken down bass levels a bit.
they're still not as good sound-wise but I chose for comfort levels and portability mainly, and the sound is just good enough for me. I got mine used at half of retail, wouldn't buy for full price I don't think.

and well... isolation is rather low on the 1R. I care more about sound leakage so that's fine with me, doesn't leak much.

I'll second the K550, especially if you can get them refurb'd by Harman for $130 like several of us did recently. I got mine today and have been enjoying them with the full range of my music. I think they sound better at medium volumes (good for working) and despite being closed, it has a rather large soundstage. There are many similarities to HD800s in that they tend toward brighter leaner, but they still have solid bass with surprising low extension. They have the big soundstage like HD800, but not as good and the highs aren't as refined. Detail extraction is good for the price, but not a giant killer. I'm listening to some acoustic bluegrass right now and it sounds good. I listened to some classical earlier and it really suited the K550. I think the K550's worst performance is with overproduced pop/rock, but then again most headphones have problems with that. The lean toward brightness makes the badly produced records fatiguing. Otherwise the only thing I can really notice with these is that vocals often have a synthetic feel to them. It isn't distracting to me as I get accustomed to it quickly and forget it unless I focus on the voice.

The K550 is comfortable enough I have worn them all of tonight, perhaps 5 hours straight so far. They are closed so there is some heat capture, but it hasn't been uncomfortable for me, no sweaty ears, etc. I do take them off here and there when moving about the house and those breaks give my ears a chance to cool and breathe. They aren't the most comfortable, but I don't have any specific complaints. Clamp is light to medium (more than HD800s), surfaces are smooth and comfortable, adjustment is easy and secure.

The HD598 is a great pick as well, but open at work would be no-go I would think.

What changed in the K550? I remember back when they were released, it was highly (if not brutally) criticised by some here as terrible.

Need some advice. I am awaiting delivery on a pair of Enigmas and Slants. I also have HD800's (stock, but waiting for the release of Anax 3.0 some day.)
For an amp here's what I am looking at:

• I own a Vali.
• I can get a used Mjolnir for $450 (It was made in 2012. Have there been any upgrades since?)
• I can get anything new from Schiit for 25% off.
• Or something else?
• Or should I just be happy with my Vali? (Is it even worth upgrading if I can't afford to upgrade to an EC or Cavalli, etc.)

(For now I am using the prototype Vostock amp/DAC as my USB DAC.)

It really depends what you want from your system.

The thing that impresses me most about the Vali is how well it does EC/Cavalli type plankton retrieval.  The downside is that it lacks smoothness and clarity/refinement.  To get the best of both worlds requires you jump up to EC/Cavalli.  Everything else will likely be a compromise on a sliding scale from resolving--smooth.  If you know where you want to be on that scale it will be much easier to figure out an amp for the HD800.

Thanks for the response.

Like I said,  EC or Cavalli is probably out of the budget.

I definitely prefer resolving over smoothness,  especially when I am using them with my Out Of Your Head software.
 I love Stax , although I am going to have Enigmas and Slants for the amp. I think they're smooth enough for me. I don't want them any smoother or softer.

It sounds like the Vali is good enough for now since I already have one. I can save up and upgrade to EC or Cavalli someday.