I am having a problem with a certain aspect of controlling my Marantz SR5500 via RS232, namely I can't get it to control any of the multi-speaker functions. Everything else is working fine via RS232 and I have full and correct feedback.

Note that I have checked the serial protocols for many of the later receiver and from what I can see they are identical, so anyone with any relevant feedback based on newer models, please feel free to chip in!

The interesting thing about this case is that I can control all the multi speaker functions just fine using IR, so I know my setup is correct (ie not in Economy mode and Surround Rear speakers set to "Off" - all correct there) and the rest of the RS232 commands, as I said, work great.

When I submit a multi speaker command (cannot remember the exact command, but it's correct!) I get a response of "15" which is a "Command NAK"

Does anyone have any light to shed on this? It's really annoying!

Marc