So.....you have a pre-made door unit in mind - OR WHAT?
You may have to fashion a welded primary frame assembly of a sufficient size that would screw to the metal studs. The door frame assembly would then attach to that primary assembly. It would still overlay the stone veneer.
Get your plan together before you go any further, don't get in a hurry. Drawing a few speculative pictures with Sketchup and really knowing what you are doing to make it all come together is two entirely different things.