davidmolliere
Headphoneus Supremus
I very much doubt Earsonics is able to develop/produce drivers in-house. "Proprietary" probably just means they are tweacked TWFK/Sonion drivers made to meet specific specs. But any CIEM manufacturer able to order quantities large enough is able to do that already.
As far as I know, Sony is the only company which had the know-how and enough cash to produce their own BA.
You can add FAD as they have custom BA for the Final Heaven's for example if I am not mistaken. But it's a valid point, it's very costly to build in house so it's probable you're right about this.