hoser,
Welcome to the forum!

The 9.3x74 is a rimmed case, and is loaded to much lower chamber pressure than the 30-06.
Both these features are desirable in a double rifle.
So long as you can obtain factory ammo or reloading components for the 9.3, it is by far the better choice for a DR in my opinion.

If ammo and components are likely to be an issue, you may have to look at the alternatives.
When it comes time to make the final choice, it's your call.