Hey, it's not a headphones sub if there's no Koss-post. And since it's the brand that brought the first stereo headphones to the world. Why not start with that.
These are mine, had several. Usually broke the cable, sometimes used the life-long warranty to get free parts.
As i got more interested in headphones, the portapro wasn't quite good enough for in-door listening as it used to be. So i made "wireless" mod so i could have something decent while running.
They are perfect, the tuning actually works better outside.
The mod was "designed" so that nothing was broken to archieve it. The cable is intact.
The BT-adapter is switchable, i have another one for instant full battery.
Adapter is in a weird angle to keep the if off my head. Found out fast how the head blocks signal and in wide spaces the audio would hiccup.
Headband has an adjustable locking mod, keeps from eating hairs.
Nicely done! Have you thought about shortening and re-terminating the 3.5mm cable, or do you like having the full length in case you want to occasionally use them as wired headphones?
I've been planning on maybe clipping the cable on my broken older pairs and remaking this. Keeping the original cable intact on these means that i can reverse them in the future. I like having one pair with a flawless cable.
I daily a KSC75 on a headband because it weighs almost nothing and I spend a lot of time at the PC. I don't use it as much for pure music listening but daily computer stuff it's all I use.
Can't beat Koss' mod-ability. I babysat a kitten for a few days a while back and he was in my lap and bit right through the left side wire like it was nothing and I luckily had a spare ready to go, just popped them on the headband and good to go in 2 minutes. Saved the broken pair, desoldered the wires and put the drivers into an OH2000 from Aliexpress. Sounds great there too.