What kind of device would you like to be added :
Harman Kardon Citation series (I have a Citation 500)
What kind of category signal would the app use :
Is there a (public) API / documentation or known other implementations (like Blogs/Github etc)
Not that I am aware of. Couldn’t find it.
Are you willing to loan or donate a device to a developer?
Unfortunately no (is a 650 euro device