I've been eyeing the 598's pretty closely -- are the 58x and 6xx good options too? Very temped to pull the trigger on the 58x, but curious to see if there are any drawbacks considering the price seems great. I read that it has a pretty narrow soundstage and I'll be starting out without an amp (relying on mobo's built in one for now), though I have no issues getting one down the road.
It almost seems too good to be true for its price. Ditto the 6xx (and k7xx). Having a hard time picking through all three. Guidance is welcome lol
If you live in the US the massdrop ones are good options yeah (as someone who lives in the UK they're not quite as much of a steal due to customs/duty being lopped on :P). I have the 6xx now and I still enjoy them for gaming. Their soundstage isn't as wide as my old 598's but overall I do enjoy the sound signature a bit more. That said I do personally have them amped with a Modi 3/Magni 3. I can still use them with my phone and they do get loud enough, but they don't feel quite as, i dunno, full in their sound. Course that could say more about my exynos S9+ than their the headphones drive-ability.
The 58x should be easier to drive than the 6xx so I'd imagine you'd be fine using them without an amp. Since I don't own them I can't really comment too much on what they sound like. As far as I understand despite them sharing the 5xx model number, they are more like the old 580s which aren't really like the 598s. Sound-stage probably won't be as good which is a tiny bit of a negative for gaming, but as someone who did move onto headphones which has less of a soundstage, it can't say I missed it too much for gaming since I tend to use surround virtualisation anyway which increases soundstage a bit regardless(i'm not massively competitive though, I do play apex and fortnite but I'm not some pro). Considering you're coming from some old Sennheiser Momentums, it probably won't bother you as they don't have the best soundstage themselves.
I've heard the K7xx is similar to the Q701 which is an upgrade of the K701 which means it's likely got a really good soundstage if you absolutely must have that, that said they may not be quite as exciting for music since I think they're a bit neutral? (don't quote me on that one)
Honestly you probably can't go wrong with any of them really since they're all well regarded. Just people have their preferences due to the different nuances of them all. It's just a shame with massdrop you can't try before you buy to see which you like most.