I have a 9C that I am using the default setting for using dual elevators.
I now want to mix my elevator to my rudder but when I do I only get channel to to follow the mix

Long time but try LINK in the mix page

If that doesn't help I'll dig out my radio

I'm not sure this is your problem but I had to remove the links in the mixes and add them in a specific order that the radio dictates. It might need to be removed from the elevator. Then added to the rudder first, then the elevator. It almost seemed backwards when I did it but it worked. Or maybe it makes sense actually. The rudder is the master for the knife edge mix. One of the elevator halves is the master for the elevator mix. So the rudder to elevator mix link should be done first, then the elevator to elevator mix link second.

yes if i remember right the rudder is master for k edge mix,,been a while since i used a mix

I am using the ailevator mix for my elevators.
When I go to either mix 6 or 7 and select the elevator for the slave I loose my link with my rudder as my master.
If I select any other channel the link option becomes available.
I'm following the book too the tee but it's not working.

Ok after playing with the radio I went into the 2nd page and eliminated any rudder or elevator combos even though they were all inactive.
I replaced them wilth like throttle, and gear. After doing that then on mix 6 rudder/elevator the link became available.