Actually 2 Texas TAS3204'sThe actual answer is probably that it doesn't much matter. All the equipment you mentioned is late model and good quality so however you hook it up it's gonna sound great. The surround master has a DSP unit in it that is very good (Analog Devices Sharc I think , ) and the Exasound is about as good as it gets. Your pdf is of a McIntosh and I don't think there would be any complaints about the sound of that either.
You are running up against one of the big problems with multichannelism. The lack of versatile preamp/processors with flexible and sufficient input switching quantity. The MX122 at least has one single RCA mch input.
What you could do is get two of these:
and put them between the Exa and the SM on the inputs and the MX 122 on the output. You will have to push two buttons to switch between them.
I have one of these and there is no difference at all between the audio and video channels except the color of the RCA receptacles. This is not elegant but will allow you to have the best of both worlds without having to rassle with cables. There are also some solutions from folks like Zektor and others that will work maybe even better but this would cost $40 to try out.