If the objective is to get the audio back into the DAW with the least hassle, yes, go with the ES-9. It'll also open up some possibilities for controlling the modular via the DAW IF you can get Reaper to speak proper CV/gate/trig/clock outputs. I would presume that the ES-9 comes with a copy of Silent Way, though, so the big question isn't so much whether the ES-9 will work, but whether Reaper and Silent Way can play nice with each other.