I got the HD598 off amazon about a week ago. These are amazing headphones but I just want to clear something concerning comparisons between the HD558 modded.
I always read that the hd558 sounded close the 598 after the foam mod but from my experience this far from true. I have had the HD558s modded for about a year so I am fairly familiar with their sound signature. I would illustrate further on some of the note-worthy differences . I'm not necessarily an audiophile but these differences where quite evident to my ears.
SOUND QUALITY
Firstly, the soundstage difference is what got my attention as this was the part people said was similar after modding. However, if the modded 558 soundstage is a 6/10, I would give the 598 a 9.5/10. The sound seems more distant, the instruments separation on the 598 is more pronounced, and you can accurately pick out clear details of each instrument on a good recording. I also own the ie80 iems. I always compared them to my 558 and felt the separation was just slightly better on the 558. However, comparing the ie80's soundstage to 598 is like a heaven and earth difference to my ears.
Now most people have said this already but the sound on 598 clearly seems more refined and detailed when compared to the 558. I'm not sure if this is due to it's better treble representation as I noticed when using eqs that increasing the treble tends to make the sound clearer. The hd558 (modded) sounds warmer and has more sub-bass than the 598. The 598 is less boomy but the bass feels tighter and controlled. I also prefer the mids on the 598. The are more forward but not so much to be annoying, just detailed and clear.
There are people who night prefer the warmer sound of the 558 as they may feel the 598 might be too bright for their taste. I feel like that when I put on my 558s but the moment I take it of and use the 598, everything changes..lol
just to add:
COMFORT
This why I still use the 558 from time to time as It's so much more comfortable when compared to the 598 and these (598) are very comfortable. It could just be due to the fact that I've had the 558s for longer while and have probably stretched them out a couple of times. This may well be a biased comparison but atm, the 558 wins in this part. I also prefer the hd558 foam head padding to the leather-like one on the HD598.
This is just my take on the modded HD558 and the HD598. This is what I can ascertain from my ears. However, I feel that most people make comparisons of these two without actually owning both or comparing the side by side for more than a day. However, people's ears are different and things might be similar or vice-versa to others. Also, I'm currently not using a dac or amp just the sound card from my macbook air 2012. I would be getting the dragonfly v1.2 by next week so I would make an update if there are any changes in their differences.