Also, to clarify, the GBOxxxx Grafik Eye wall plates accept a Beo 4 command natively, so this operation doesn't rule out any issues upstream to the BeoSystem 3 via the GRX-AV. You may already understand this fundamentally, but the GRX-AV is sending the signal from the "RS-232" (actually mux-link) D-sub 9 output on the BeoSystem 3 to enable light scenes when FORMAT 0 is pressed.
There is scarcely anything in this world that some man cannot make a little worse and sell a little more cheaply. The person who buys on price alone is this man's lawful prey. - John Ruskin