psand: The MCP6500 uses a different data link address than the BL5000 and BL7000.
Well,
yes and no. I just tried. The MCP sends the longer (two-way with its
own address) commands, and the BC9500 executes them just fine, so you
can turn it on, select sources and tracks, turn it off, etc. However it
never sends back a response addressed to the MCP.
This means that
the MCP won't allow another keypress until it is convinced that nobody
heard it, and shows "NO CONTACT". Therefore you can't select any
two-digit commands (like radio preset 18 or CD track 12), because the BC
times out waiting for the other digit before you can send it.
And
yes, the volume is hopeless - because of the same timeout issue, it
runs like you had a mile long rubber band in between, and ends up all
over the place.
Stuff that absolutely requires two-way (like programming) is obviously totally out of the question.
All in all, useless for anything else but emergencies.
***
If the software in your Beosystem 2500 was only prepared for 1-way communications, it probably ignores two-way commands completely.