Focal Elegia Circumaural Closed-Back Audiophile Headphones Expired

Good sounding headphones, but beware durability concerns. Even people who've babied them have had major failures, I believe it's the headband causing issues.

Best way, without jailbreaking, is to get a Qudelix 5K. It's by the man who made the ES100 that took the headphone community by storm several years ago. He split off to do his own thing, which was Qudelix. Really amazing little device and you can tweak everything through the companion app (also has a chrome extension that does the same). Then apply the oratory1990 EQ settings someone linked above. Or if you dislike the Harman target, use AutoEQ to spit out an auto-generated EQ profile for w.e target curve you like.

Apple has always had very little codec support for BT (AAC and SBC, and very rarely, ALAC), so if you use bluetooth, audio quality will take a hit. Whether or not that bothers you, is up to you.

If you dislike that, you can use it as a dongle (you just need to get your own USB C to lightning cable (or adapter) as they only provide USB A and USB C to C).

There's also the option of finding some way to velcro or otherwise stick the Qudelix to the headphones (these are closed back, so pretty easy to stick it on the sides or on top of the headband). If you stick it on the side, you can use the Qudelix's mic as a headset. Just be aware that the mic sucks (though a fun feature they added is that you can enable the mic while connected via USB).

Other optional longer term upgrades: you can get a balanced cable to connect to the Qudelix's 2.5mm output. Not going to get into details, but balanced essentially doubles power output because it has two in-phase signals instead of one (unbalanced) [boxcast.com]. Dedicated amps generally don't lack for power, and outside of very very long cable runs, EMI on unbalanced doesn't matter. But for portable devices, which are power limited, balanced provides a pretty large power benefit. Shouldn't need it for this pair, but harder to drive headphones would receive some benefit. Just never plug a non-balanced audio device into a balanced port.

You can also use the Qudelix 5K as your desktop dac/amp, or as a preamp (to enable EQ and other settings) to a dedicated amp. You would enable car mode for that; their website has great guides and the support team is very active on the forums.

I use mine for both on the go and on my desktop; I have a USB C cable fixed to my desk that I plug it into. Nice thing about doing it that way is that it'll always be charged for when you want to take it out for portable use. Though you can set it to charge from your phone (or not) or just use a portable charger.