CFCNX's question:
By holding the outer left button you will come in the menu where you select the kind of screen and it's rotation. Here you can configurate your scroll sequence, but also which screen will be the boot screen. So having no NAV display for the GNS430, as you describe, I would select the HSI as the boot screen and the EFIS the second in the scroll sequence. Once this set up is done, you can simply touch the outer left button and the page on the Dynon will change. You still can go in this menu in flight, if you like to change it, by simply holding the button again for a short moment.
If you have no CDI to select the OBS on the GNS430, you still can do it on the Gramin. Just hit OBS, move the crusor over the course readout and twist your desird course, then hit enter. Your Dynon HSI will then move to the CDI simultaneously with the Garmin's display.
Best regards
Thomas