Yes. The EX6 has 3 grates and the EX4 has 2.My after-market stainless grates from my Genesis Silver B fir perfectly in my SF EX4. I wonder if 2 gas grill grates would work. Do the EX4 and EX6 have the same grate length? If so, I bet would work.
I too generally use them on the "Flat Side-UP" on my Weber Performer Deluxe and Weber Smoky Joe.'m very happy with them but tend to use them upside down to get more meat seared. I don't worry about grill marks.
I set them up to the right of the fire box, flat side up. It works for me at 500° but I think you want more searing than I do so you might go to 600°. My 3 GrillGrates measure 15" by 15" and that gives me a grilling station for the 2 of us. You may need bigger. Just give them time to get up to temp. I check their temp with a laser therm..Bumping this up. Anyone use grill grates on their smokefire? I don't care much for the "grate" side, but the "flat" side would seem much better at getting an even sear.