I have the CM GT and we had an Britax Chaperone car seat. We were able to use an adaptor (I'm not sure what one but it was specifically labeled to say it would work with our car seat). I got it from my brother/sil who used it on their Baby Jogger City Elite. It looks like a pain, but it snaps in pretty easily. Basically, two "bars" click into holes on the strolle. It might be the one you're looking at, or maybe it's the one you think looks bulky with the aluminum rods. If you include a clicky to it/them, I can let you know for sure.
I will say this, though - while it worked, I feel like it made the stroller bulky and top heavy. Not unsafe, per se, but once we started using the stroller without it, it felt so much easier to maneuver. If I had to do it all over again, I would have bought a Snap N Go to use with our infant carrier. (Still buying the GT also because I LOVE it!)