I have the TDS 750/650 installed in the arrows.
I understand the 750 is linked with Nav1 and the 650 is linked with Nav2. From the 650, the com frequency can be changed but I cannot see anywhere to toggle this to actually enter a NAV2 VOR. I have a workaround that I can get out of the 750/650 unit and move over to the older 100 and then set Nav 2 from the radio. However, I was thinking there should be a way to set the Nav2 frequency without changing the entire radio package.