Official comment
The RB-DMX1 is not discontinued, but rather on short supply due to difficulty in obtaining the necessary parts for production thanks to the global silicon crunch.
You can't add your own fixture, but you can ask our lighting database team to include it and it's usually added to the rekordbox database within 2 weeks.
The computer is required because of the lighting programs themselves, and none of our controllers are capable of storing the lighting fixture library / macro library / hosting the DMX device.