Thanks for your reply Johan.
I’ve read that the surroundmodule in the av9000 is non-digital and really supplies more of a pseudo-surround experience than a proper one.
Since the IR receiver is mounted on the screen, there is no (easy) way for me to just control the audio unit without the CRT.
Switching on the speaker unit without a connection with the screen results in an error code on the display on the speaker. The screen however functions without the control unit.
I’ll post some pictures in the evening when I’m home again.