You get either/or, not both. If you want or need six burners plus the charbroiler you'll need to opt for the 48" model.

We got the 6 burner and plan to use a Lodge grill pan/griddle on the rare occasion...just seems much easier to clean and more flexible, and I noticed that's what all my favorite cooks on Food Network do, too.
We've found ourselves using 5 of our 6 burners quite a bit over the holidays! (Haven't used all 6 at once...YET)

I agree with c9pilot. We put in the 36 inch range last year. Love it! And we have the Lodge grill pan/griddle for when we need it. Works great. I don't know if you can opt for 6 burners and change them out to a griddle later. Good question, but our set up works very well.

We got a 36" Wolf with the charbroiler in the center. We don't really need more than 4 burners at one time, and the 36 inch allows us to use 4 rather large pans at once. The grill is great, but we don't use it more than around once per 2 weeks. Clean-up is not an issue grilling fish or sausages. The charbroiler works really well to grill and blister chiles and to grill vegetables. We grilled a flank steak for fajitas one time and I was not pleased with all the smoke and the increased clean-up work. I haven't tried grilling a steak or pieces of chicken yet.

I would also note that the hood requirement for the 36" with grill is greater than for the 6 burners. We really stretched the limit by putting in a 36 inch ventahood over ours. For the flank steak, I'd say it was really pushing the limit and we did open a window. For fish and chicken sausages, which we grill much more often, the ventilation from our 36" hood is definitely sufficient.