It depends on the goals.
If you are looking for a headphone to travel with that wouldn’t be a disaster if it got lost/stolen/damaged then the 599se might be a valid choice.
If you are looking for “a step up” then spending less than the 660s probably won’t get you there.
It’s a big gap from from the 660s range to the next level, usually something like the Clear, 800s, Hifiman or possibly the new Meze 109 Pro.
That’s the reason to get exited about the HD59x series and similar tier Sennheisers. Combined with the fact that you can drive those headphones with modest amps/sources and get that great sound. You can use the HD59x with general consumer sources like a laptop and they will sound good. You don’t need a $500 amp to get them to sound up to their potential and sound good.
Contrast that with the higher tier Sennheisers like the 300 ohms HD6xx. Those need an amp to sound good. Plug a HD6xx in a laptop and the HD59x or HD660S or Drop HD58x Jubilee will sound better. But plug the HD6xx in a good amp and source and the HD6xx will be so much noticeably better.
I have the Drop HD6xx and also the 150 ohm Drop HD58x Jubilee and also multiple pairs of the sub $100 64 ohm Brainwavz HM5 and Monoprice HR-5C (currently $31 on Amazon on closeout). I have the Brainwavz and Monoprice because they are inexpensive, sound good, and sound better than the HD6xx when using my laptop. They even sound better than the Drop HD58x Jubilee when using my laptop. That’s why I have them. That’s why I use them. And they get a lot of use for YouTube listening. Sometimes more listening time per day than my $1K headphones. And that’s why I have them and that’s why I use them.
But use those headphones in my good amps it’s like why? With my good amps the HD6xx is very obviously better. When I try the HD58x Jubilee or Brainwavz/Monoprice HM5 in the good amps it’s like why? Why would I listen to these headphones with these amps when I’ve got the HD65x and HD650 right here? Why? (And then I ask myself why would I listen to the HD650 when I’ve got my Audeze headphones right here). I hardly ever listen to my HD650 and HD6xx and the H58x Jubilee because my listening is either laptop with the Brainwavz/Monoprice HM5 for YouTube or my Aueze using my big amps. The HD650 and HD58x and similar headphones in my collection exist in no man’s land, why would I go there when I’ve got better choices at either end.
I will keep onto the hd599se I have a feeling I will grow to like them more as I use them more due to the convenience. My ears have some what already adjusted slightly.
I’ve found that – as a rough rule for many headphone brands – price often does indicate quality. In my experience this holds true from ultra cheap $20 headphones/IEMs up to perhaps $2,000 items. A sub $100 item can be tolerable, but typically has obvious limits and flaws. A $100+ item will sound good, $500 a lot better, $1,000 better still, and $1,500+ usually sounds quite excellent. Above that, small production numbers, overhead and build cost differences, and luxury marketing make price/quality comparisons tough.
The HD 6XX is the most glaring exception to the rule, as Sennheiser and Drop accidentally created a huge value product at $200 to $250.
Sennheiser specifically stratifies their 500, 600, 700 (it didn’t do well), and 800 families by price and quality. The 600 family scales while the 500 doesn’t. The 800 family has better extension, staging, and clarity than the 600 family.
Be careful about wasting money on ‘sidegrading’ – or spending about the same money on a new product for about the same performance as your old one.
A guy on reddit actually bought the HE-1 system and unboxed it
That headphone unboxing video randomly made me think of the Ferrari in Ferris Bueller’s Day Off:
Boosted bass frequencies & 300ohm ………
I have the HD 800 s as well. Really comfortable,
less temple head pressure than my HD 6xx.
The Soundstage is much larger, layering of instruments is very good. With balanced cable and a good dac/amp the sound and detail retrieval is amazing. I truly believe Sennheiser has some of the best engineering around headphone design and sound quality. They have set the bar high for other companies to compete. If you look at the HE-1 and the technology used to create the most expensive headphone on the market, its hard to imagine a better setup for sound quality. Sony has a similar offering with their signature series, but is not at the level of HE-1.
He-1
I do not know. If these headphones need a burn in period, but if its a tube amp i would say yes.
This is why i feel sennhieser is the best headphone on the market today. What other company has the engineering and experience to create something so amazing!
If you have trouble with youtube link just type in “HE-1” by joshua valour.
For anyone interested DMS was given a couple HE-1s courtesy of Sennheiser to play with. He laughed, he cried, he dropped one and broke it. Check out the start of his HE-1 journey!
“He dropped one and broke it”? 
I need to hear more. lol
btw, I don’t know if DMS has spent any time with the Hifiman Shangri-La Sr, but if he has I’d be very interested in hearing thoughts on how they compare. It seems everyone has heard one or the other, but rarely both.
As someone who has heard the HE-1, Shangri-La SR and Aperio I can tell you the number one cold, hard fact about them that you probably wouldn’t hear from anyone else if they’re being honest.
I will never be able to afford one 
I’d take Shang Sr over HE-1.
Had one hour with HE1 at my house with my music and source. It was great fun and it’s very good but a bit media hyped.
I thought you were going to say that they all perform the same after being dropped on the floor.
I purchased some after market earpads for HD 800s. I also got a 16 core occ cable for comfort, Soundstage, Bass. I think it really improved the sound and comfort 
Might be placebo effect, but i love the lambskin pads, and the cable is lightweight and so much more comfortable and attractive. I find stock cables to be heavy and dull looking!
They certainly look good on the HD 800 S - Which pads did you go for?
Thanks, I went with soulwitt on amazon cheaper then dekoni, and they use memory foam, so it feels more comfortable. They also included a plastic tool, which made removal much easier.
Sennheiser HD490 Pro new for 2024
