How about a dongle that can drive your headphones? I heard the Lotoo or Luxury [something] W2 are the best options right now. The Apple dongle is good too if it can drive yours.
It does sound like you really prefer the convenience, maybe more so than purely sound quality. The Apple dongle is dirt cheap if you want to give that style a try for a few days.
Personally, I was happy enough with the Apple dongle, but I used it with IER-Z1R. Regardless, I like ZX300 sound better with it so I'm using it right now and I'm not going out much with COVID. From a usage standpoint however, having a true wireless or dongle when going out is still better. Like I said, maybe you can give it a try since you knew those things are personal preferences. Might as well just do them yourself
P/s: if budget allows, won't you entertain the idea of having both? like ZX300 for office/home/picnic and Airpods Max for outside. For me, there's times I just want to shut off the outside noise for a moment and just listen to music (mostly during the weekend with a piece of steak and a glass of wine, maybe movie).