[1800 mW] The HD 800 S is very comfortable and feel exactly the same as the old HD 800. The sound stage and imaging are amazing (like before) and Sennheiser (finally) fixed that high peak and added a little more power to the bass. However, I feel that they are still as picky in terms of amp-pairings. Definitely do your homework on pairings (try them out at a local hi-fi store/audio meet) before dishing out for these. They may sound fine on some amps but are lackluster on others and require more power than most other headphones out there. Accessories are the usual except they now come with the balanced cable -- which used to cost $400 separately. I can't comment on the difference in sound between the unbalanced 1/4 and balanced XLR cables as I haven't spent the time to A/B test them, but it's nice of Sennheiser to include this if you ever need to switch to an amp with only balanced outputs. The included cables are a bit long if you're not in a studio, but if you have the money for this pair of headphones, you can probably afford a custom, shorter cable for portable/at-home use.

[1x 1/4" TRS] Amazing. Just amazing. Takes me back to my dedicated hi-fi days. Not hyped, just awesome, clear, detailed, and spatially enveloping. Unlike some other reviews I've seen online about these (and yes, I looked into a lot of boutique cans reviews and discussions) I do not find a lack of low frequency. But then I was looking for a proper reference. Another reviewer here mentioned Schiit Mjolnir 2 ... I had no idea about that, and ended up going that route as well. Definitely worth it. I will say I was a little let down with the lack of significant obvious difference between the unbalanced headphone outputs of the two interfaces I use (from computer, an Akai EIE Pro and a MOTU UltraLite mk3) ... but when I switch the included cable to balanced and listened with the Mjolnir 2, I started to get it ... seemed that the depth and detail increased. To be honest, it had better ... I WANT it to make a difference. And of course it's a little harder to A/B since one has to switch the cable out. For what it's worth, I listen for general use and reference with the LISST cans in the Mjolnir, and when I want pure enjoyment and exploration, I put the tubes in. Between the LISST cans and the tubes, it is more apparent in the HD 800S than in my other cans, which sound midrangey and hollow by comparison ... also, I find it MUCH more easy to hear overcompression and small distortions that I would not have heard otherwise, so just that, by itself, is a case for the Sennheisers with or without fancy amp. I am happy to say that things are less disturbing or surprising when I listen on speakers after working on stuff using the HD 800 S ... so, for what it's worth, as reference cans, I find them very satisfactory.

[Stereo] Pros: The best compliment I can pay these are this: When I listen to music on them, I have yet to wish for more treble or bass or vocal clarity. They disappear on my head and I can just truly enjoy what I'm listening to. For the price, especially compared to the cost of other planar headphones, that is epic. Cons: I would suggest watching Z Reviews' Youtube video on all of the Mk3 headphones to get an idea on the differences and comfort mods between the three. (https://youtu.be/SpRCK6CVdis - Children beware, there is swearing in the video.) I think his review is spot on, in just about every aspect of this. (Disclaimer: I haven't heard the 40RPs, just the 20's and 50's.) First Con: The stock earpads. They are super thin, and not very comfortable - but to be honest, not hurtful. They are essentially ON-EAR headphones with the stock pads, as your earlobes will make contact with the inner driver area. The Shure HPAEC1540 and 1840 pads are hands down the most comfortable and best sounding pads I've found for the T20RPs. I like the 1840 pads just a bit more than the 1540. Second Con: The headband is thinly padded. It isn't uncomfortable, but can be improved upon. I went with the Mr. Speakers leather headband, and they just float on my head now. No pressure points becoming sore after hours of listening. The hardest part of installing this was figuring out where in the house I left my screwdriver. Third Con: Sensitivity. These are not easy to drive. Your smartphone will not suffice. If you need an inexpensive amp, I suggest the Micca OriGen+, or one of the many Fiio products. I listen to mostly rock, classic rock, metal, edm, blues, and a limited number of jazz and classical tracks. I would describe my listening preferences as being 1/2 way between bass-head and audiophile. I love bass, want it loud, but do not want it trampling over the rest of the music. I purchased the T20RP Mk3.

[Gold] Headphones are incredible; get a nice headphone amp to help them shine but awesome headphones

[5 Hz to 45 kHz] These headphones were an upgrade from my HD650 headphones and I can safely say the upgrade was worth it.
If you are looking for the best premium HIFI headphones on the market for less than $2000, these are it.

[1800 mW] If you want to mix in an untreated room, this is the way to go. Even just listening music is a total experience with these, you can hear multiple levels and where they are supposed to be, real nice. For the price they are worth it over treating a room, especially if you are modular with your studio.

[3.825 lb] great head-phone! If you listen to hiphop,r&b or any music in general, you need this. Bass is deep, both mids and highs are great. Headphone works ok with your mobile devices, but you will ge greatly rewarded if you power this with a amp.

[1x 1/4" TRS] Excellent build quality, very premium feeling. a bit heavy but not a deal breaker for me since it's quite comfortable.
I tried Sennheiser HD650, too warm for me, the veil is real and I don't like that mellow feeling. I also tried beyerdynamic DT 1990 Pro, while I love the soundstage and crisp sound, the treble is too sharp for my taste, every sibilance annoys me.
So my goal was to find a balance between two, a perfect combination of those two. Focal clear hits that exact sweet spot. I know they're not in the same price range but I like what I hear from clear from first moment. The only compromise I'm making is...well, cost.
I'm using a very basic schiit stack and based on my research and what I hear, it's enough.

[Gold] I picked these up after a friend had nothing but good things to say about them for a year. They have changed my listening experience for the better. Every time I listen to a track I swear I am hearing something new. If you're in the market for some great headphones and have a decent amp, then you can't go wrong.

[2" / 50 mm] Though I'd had the HD 800S headphones in my wishlist for a couple of years, I always balked at the price. I already own several high tier headphones from AKG and other Sennheiser models, and I figured the difference would be modest in an upgrade to the HD 800S set. I was wrong. The difference in spatial perception of the sound field is immediate and pronounced. Doing an A/B comparison with my other headphones, you don't have to listen too carefully in order to hear the dramatic difference. In addition to the outstandingly realistic sound field, they are extremely comfortable, yet solidly built. Outstanding on every level. My only regret is that I didn't order them a couple of years ago.