My 421 also has the usual Meridian Din type Comms socket. I've used this to control the source switching on the 421 with a standard comms cable from my G91. (Note I intentionally didn't plug the G91 into socket 4 because which detects a Merdian Player as I was trying to get around a problem with my display). This comms connection worked fine with the G91 so I can't ses a problem using a G68. Even so I now use the RS232 to switch the 421.

Current Mismash of components :
1) TV System Living Room
2) Media Streaming Kitchen
3) Cinema System
4) Media Streaming Room 2
5) Other stuff in the post...