If I remember right, they send everything to the computer (running logic) first for effects processing (they have UAD1 for example and use it alot) and use the analog desk to finally mix the whole project. They don't use the Logic's digital summing but send all the tracks to the desk and mix in analog form. They may output some of the synths directly to the desk too but I'm not 100% sure.
Kill me if I'm wrong.
In fact that's something I will do someday too...