[papant7]

Having tried the 598, 600, 650, 700 and 800 I actually loved the 700 the most. 
 
Take note that I am very sensitive to harsh treble and I found the 800 to have the worst treble.  I used it with Burson Conductor, I expected a lot for a flagship headphone.  The 700 was the best among the bunch for me.  This time I powered it by go dac with lineout from an iPod touch 5th gen + lightning to 30-pin to USB.  It was a lot more fun and it was more bassy.  The hd800 had a far more wide soundstage.  It was also the most airy among all the Senns.  The 650 and 600 are quite the same that I spent little time listening with it.  (same setup with hd700) Also since the hd700 was there I had much more fun with it.  I loved the looks too.  The lightest among all the cans too.  The 598 is more of a little bro of 700.  Much like the 600 to 800.  The sound sig of 600 is closer to 800 than 700 since they are flat sounding and not fun sounding like 700 and 598.  The 700 has hot treble but is not so harsh for me. The 600 and 650 are heavy due to their construction.  I currently have the 598 and if ever I will buy a new Senn full size open can it would be the 700.  Very easy to drive too.  I used it straight out of the touch with no problems.  All headphones were tried using their default cables

 

[jmarsiglio]

I agree with papant7. I've tried all the phones he mentioned and my favourite is the HD700. I love my 598s but the 700s I won't hesitate to buy once I find a good deal

 

[DannyRox23]

I have recently purchased the HD 700 and think they are well worth what I paid ( 600 USD. ) In my opinion, the HD 700 sound more like the HD 650 other than the HD 800. The only signature borrowed from the HD 800 are the mids because the mids are almost identical. The sound stage is not as vast, but it's there ( sounds more like the instruments are vibrant/detailed other than wide/vast. ) The HD 700 pretty much has the same bass ( a little more defined ) as the HD 650. However; the highs come off unnaturally ( the only downside. ) I think the highs is what makes them sound "fun."

  Having tried the 598, 600, 650, 700 and 800 I actually loved the 700 the most. 
 
Take note that I am very sensitive to harsh treble and I found the 800 to have the worst treble.  I used it with Burson Conductor, I expected a lot for a flagship headphone.  The 700 was the best among the bunch for me.  This time I powered it by go dac with lineout from an iPod touch 5th gen + lightning to 30-pin to USB.  It was a lot more fun and it was more bassy.  The hd800 had a far more wide soundstage.  It was also the most airy among all the Senns.  The 650 and 600 are quite the same that I spent little time listening with it.  (same setup with hd700) Also since the hd700 was there I had much more fun with it.  I loved the looks too.  The lightest among all the cans too.  The 598 is more of a little bro of 700.  Much like the 600 to 800.  The sound sig of 600 is closer to 800 than 700 since they are flat sounding and not fun sounding like 700 and 598.  The 700 has hot treble but is not so harsh for me. The 600 and 650 are heavy due to their construction.  I currently have the 598 and if ever I will buy a new Senn full size open can it would be the 700.  Very easy to drive too.  I used it straight out of the touch with no problems.  All headphones were tried using their default cables

 
I don't have the HD 600, but I do have the rest you listed in the first paragraph ( along with the 380 Pro and HD 518. ) I agree what you say, but the HD 700 sound nowhere near the HD 598. The HD 700 sound more like the HD 650, to me ( as I stated. ) HD 598 has muddy bass, exaggerated mids, and decent highs ( along with artificial sound stage. )

 

[Stanfoo]

I also have the HD598 and am looking to upgrade to the HD700.
 
Anyone else have any input on this?

 

[kekoukela]

I recently got the HD700 coming up from HD598. I'm currently using a Magi/Modi combination for both headphones. 
 
My experience is that the HD598 were good headphones with good soundstage. I really enjoyed my music and it sounded full (warm?). When I upgraded to the HD700 the treble range became clearer. Much clearer. I could hear the individual instruments much more clearly that I did with the HD598. I can see why people did not like the tremble spikes because it is kinda loud (when listening to classical music) especially the violins. The lower ranges felt more muffled than I would like.
 
That being said, I think part of this issue MAY be my amp? It's just too entry level to drive the HD700 I think. Or that's at least what I have surmised by looking at all the forums. As you have the asgard I think you would get a better listening experience than I. Currently, I'm trying to find a better amp to drive these HD700. All in all though, I love these headphones and would suggest you upgrading. You'll love the intricacies of the instruments if you listen those genres.