I just heard from Bryton. Apparently the serial interface isn't needed and it can be done through the web interface. Just connect up with an ethernet cable and type in the ip address. A neat UI appears. Click on the "Terminal" button and type in the command.
What a shame the manual doesn't mention this.
Anyway, the display now looks ok and I can enjoy listening without being dazzled.
Sorry Bryston, I was getting frustrated. The BCD3/4BSST2/BP17 setup sounds fantastic.