I got it working right after I posted
I simply set output to 4.0 and set mixing to jrss.
I have a more complicated question about using ASIO and channel assignments. I need to route 8 channels without a center/sub (the center has already been mixed into the front channels, and the sub discarded), into my four speakers. The channels will be 1 to 1, 2 to 2, 3 to 3, 4 to 4, 5 to 1, 6 to 2, 7 to 3, and 8 to 4.
I have used the add channel feature in the peq options. The first 6 channels mapped correctly but I can't get the final channels, 7 and 8 to output anywhere, including the rear speakers, where they are supposed to go.