I got the H598 a few days ago from an audiophile friend as a gift, and I couldn't be happier with them. Even plugged directly into my laptop, the sound is excellent. I've always loved the warm, smooth mids on these. I find myself leaning toward music that compliments the phones, such as classic rock, light modern rock, acoustics and vocal-centric recordings particularly, however I've listened to a fair bit of hard rock, metal and electronic in the last couple of days,and these cans are certainly performing.
Before I go any further, I'm not an audiophile (yet). For me, the music comes first and foremost. Equipment is for enhancing that enjoyment, and my opinions will be colored by that. I've listened in the past in short doses to the HD598, the AKG Q701 (On a Schiit Magni), the Hifiman HE-500 (On a Schiit Lyr), and prior to the 598, my listening was done primarily on a Turtle Beach X12 gaming set, which I still use. The particular set of HD598s that I now own was pre-owned and has had ample burn-in time, so that factor has been removed for me.
Now that I have that out of the way, my impressions aren't exactly groundbreaking and most have been covered in this thread by someone or another, but I'd like to share.
My first impression (aurally) when I put these on last week after some time off of hifi was the bass. While it certainly rolls off a fair bit in the sub-bass, I fell that it is very much present and audible. It extends fairly low, and it is tight and controlled in a way that initially fooled me into thinking they were hitting harder than they were. As it turns out, I had gotten used to the looser bass on the X12, and mistook the tighter punch on the 598 for impact. I'm finding the bass on these perfect for rock and metal, as they boast a tight, punchy bass that's a lot of fun with double pedals! I do feel a lack of impact with electronic music. All of the frequencies are there, but they simply lack an impact, particularly in the sub-bass, that's a significant part of my electronic experience.
After a few days of listening to these, the things that drew me to them in the first place are only more apparent. The mids are gorgeous to me: vibrant, smooth and clear. The highs are fairly clear if a little recessed in favor of the mids, and sibilance has been a non-issue thus far. The instrument separation is excellent: everything has a clear sense of place and of space. Listening fatigue is not an issue with these, and of equal importance - to me, at least - is comfort. These deliver the most comfortable listening experience I've had with headphones. The headband is light and airy, the velour pads are soft and smooth, and the whole apparatus is very lightweight - and the comfort lasts. I've had some fairly long (eight hours or more) sessions with these, and there is no sense of relief upon removing them (something that was very real after a long session with the X12). My only nitpick is that my ears do touch the backs of the cups, and I'm still a bit spoiled by the no-contact, massive cups on the X12.
All in all, of the small handful of full-sized headphones I've had the opportunity to try out, these provide the best listening experience for my needs: comfort, a balanced sound, smooth mids, and no fatigue. The next step is amplification of course. I've been leaning toward the Fiio E7, as it's portable and cheap, but I'm open to suggestions.
Thoughts?