I'm confused. If KZ is subbing out the build to someone else... that someone else is the OEM and KZ are the designers in that relationship, yeah?
I used to manufacture my own automotive performance racing parts. I would do all of the design, engineering, prototyping, and testing. Then I would sub the final machining and welding to one shop, the electroplating to another, the powder coating to yet another, source the fasteners from a different supplier, the packaging from someone else, etc.
Then when I was all done I would do the final assembly, marketing, sales, and vendor/end user support (as well as continual product development).
It’s how quite a bit of manufacturing takes place. I don’t see headphones being any different.
Some processes could be done in house - for example I did some of the welding and finishing work too because I had the equipment.
So if KZ has the CNC machines, they could make their own ZS6 shells for example. Maybe they do, maybe they contract it out. China is brimming at the seams with factories (and even whole cities) that specialize in cables, other that specialize in plastic casting, others that specialize in fasteners, etc. So there’s no shortage of specialty places you could sun contract out a part of the manufacturing process (to someone with more specialty in that area, of with a huge capital investment in machines, etc).
My philosophy was always “let me do what I do best, and I’ll let you do what you do best.”
But even if they source drivers from a supplier vs manufacturing them in-house, they almoat certainly do the design, engineering, and assembly in house. They certainly handle heir own sales and distribution themselves. They are also an ODM for other people.
That doesn’t make them any less respectable as a manufacturer in my book.
That’s what lean, JIT, etc manufacturing is all about.