Im not sure if there's an obvious, easy fix for this, so I'll have to ask:

The right channel of amplified "SPEAKERS 1" DIN-connectors is dead. Both channels work fine on "SPEAKERS 2" -connectors, so the power amplifier unit is probably OK - providing that the system doesn't have an independent amp unit for each of the four speaker connectors.

The speaker wires may have shorted at some point and not knowing how the protection (if there's any) against that has been designed, I'm out of ideas. I only have a fairly superficial knowledge of electronics, so the schematics in the service manual weren't very helpful.

I'll be using the 9500 with a separate power amp so fixing this is only a matter of principle, not an absolute neccessity. I'd like to do it anyway.

Probably a classic muting relay fault - speaker output 1s go through the relay, 2s don't. Both of them indeed come from the same amplifier outputs.

Not very expensive to replace, but getting physical access to the part requires quite a bit of dissassembly. I would leave it be, if you can live without the muting function...

That was quick - thanks!

I wasn't even aware of the lack of muting function in 2nd speaker outputs until now. It sounds like I'll leave it alone, too much trouble when the only reward is a warm fuzzy feeling knowing that even features you'll never use, work.