Thanks for the advice Robbo. The 7XX looks like a good option, but they seem to be relatively rare. I wonder if the bass on other AKG headphones, for example the 702 or 712, would respond well to EQing?
If you're patient to wait for the next time that Drop get a manufacturing run of the K7XX then all is good in terms of that recommendation of mine, but I was aware that they currently don't have stock, so they're probably waiting for interest to build for a next production run, so express your interest on there at that link I gave you....you can click on one of their "buttons" to express an interest in a purchase.
Regarding the other AKG K7 series headphones point that you bring up, I did tell you that my K702 was my favourite headphone out of all the ones in my signature (bottom of post). Regarding how the K702 responds to bass boost, I think it responds well to bass boost. For my open back headphones I've got 3 that I compare against each other re their ability to accept bass boost via EQ, and the K702 sits in the middle.....the HE4XX is the most superior at bass, K702 second, and HD600 a fairly distant third. EQ'd bass is really very good on the K702 in my experience. One thing I will say is that I think there is a fair bit of variation between units of the K702, I have two units of the K702, one from 2015 and one from 2020, both are made in China (so not the Austrian made version, even older). Yes, so Oratory measured my K702 from 2015 and today I received that unit back from him in the post, and his EQ he did for it is absolutely sublime when used on that headphone, absolutely sublime....yet not quite in the same league when used on my newer K702 from 2020 - so I think this is unit to unit variation.....so that's something to be wary of when buying the K702, his EQ is still good on my newer K702, but not quite in the same league. I'm gonna send Oratory my new K702 for measurement so we can get some proper confirmation of unit to variation. If you were willing to go the extra mile, what you could do is buy a K702 and send that to Oratory as well, he's normally quite happy to measure additional units, so you might be able to end up with an EQ from him that is personalised to your particular unit that you've bought (but you'd have to ask him if that's ok re testing another unit as well as receiving a personal EQ for that particular unit)....he's a very approachable fella & very knowledgable.....if you're interested in speaking to him find him over on reddit....yes so you could end up with your own personal EQ for your particular unit which would sidestep unit to unit variation:
https://www.reddit.com/r/oratory1990/
He doesn't charge for his services, just postal fee....but of course he's open to receiving any additional donations via Paypal, mainly I think he's doing it as a hobby and as a service to headphone enthusiast community, which it undoubtedly is.
If you're a total bass head it might be better to get the K7XX because it plays louder bass naturally without EQ so likely to have better distortion figures when hitting a certain bass target, but if you're ok with Harman level bass then I think the K702 is a solid option in my experience....the added bonus of the K702 is that it has great soundstage, possibly attributable from it's angled pads (amidst it's other design features which it would share with the K7XX) whereas the K7XX does not have angled pads......so there's potentially a trade-off to be had there. I'm always banging on about the K702 so I hope people aren't getting sick of it, but I initially recommended you the K7XX due to it's open backed bass abilities originally.
Regarding K702 & other K7 series headphones I probably should do my due diligence & say that there is a weakness in the factory solder job of the wires in the earcups. The solder failed in my right ear cup on my 2015 headphone two or three times, and I was able to teach myself how to solder with Youtube vids and a £12 soldering iron to fix it.....and none of my own soldering has failed to date, I replaced all the wires & solder in the right ear cup, haven't had to replace anything in the left earcup (Youtube vids showing how to solder K702). So there are some longevity risks with K7 series unless you're quite technical/practical and happy to learn to solder. Of course they'll honour your warranty if you don't want to do it yourself, but then it could fail again, and is probably less hassle fixing it yourself if you're quite technically minded & practical.
EDIT: before taking the step to send Oratory a headphone for measurement, it's probably best to know whether or not you like the Headphone Harman Curve because his measurement equipment & EQ target is based on that premise (ie try his EQ's for any headphones you may currently own) . This is largely more of an anatomical variation (in HRTF) than a purely psychological tone preference you might have for various
speaker curves (not headphones). Most people like the Headphone Harman Curve though as proven by research, so it's a good punt if you're not familiar with it.