Well I don’t really know how stereo processing works. It was my assumption that since there are stereo inputs, which in my mind means two different, unrelated signals sharing the same ground, to compute the wet signals you had to do that processing twice (although probably in parallel), once for each input, regardless of how you mix them in the outputs.
From what you are saying that’s not the case. How can the processor do the work for two different inputs without doing it twice? Does it operate on a single signal where input 1 and 2 are added?