Hi Jon,
Boelab speakers should only have a direct connection to one device, as you can end up with unwanted noises and interference through the speakers if you try to link them directly to both devices via a splitter (the splitter is only for linking multiple speakers to one device).
Instead, for best results, please connect the speakers to the BV11 TV with two RJ45 to Powerlink cables:-
link
You can then connect the Beocenter 9500 to the 9 pin AV input of the TV with this cable to share the speakers (there is no need for a converter if the Beocenter is in the same room as the TV):-