But you talk about comfort and you're right about HD5-series being one of the most comfotable cans in the world. However when it comes to build quality that's definetly not the case. I've had many HD5 headphones and the built quality is mediocore at best. Sony use high quality plastics not Sennheiser. Depending on the unit some HD5 can be very squaky, rattly, some plastic parts are scratched out of the box from factory and all of them have cheapo plastic headband, which gets sctatched super easy and quick just from adjusting it.
The thing is 598 are very different than 599... one being mellow bass light, distorting at high volume, super wide soundstage. While the other more aggresive, less wide sondstage, much punchier bass with no issues at high volume and better detail retrival. To me 599 is very similarly tuned to 58X.
Haven't listened to new seens yet, however I think 560s are still enough different to X2HR just like 58X, 599, HD6, to own them both. X2HR have that airyness, openess to the sound being super wide no other senn have. Bass in fidelio's is also much more organic to any senn I've listened to.
599's was for 99 euros on Prime Day few days ago, and I grabbed them last year's Prime Day for even less (79E at the time). I expect 560s to hit similar sale price next year. I'll happily snatch them at that price and have both for less than 200$