Ok, I've got 2 SVS CS Ultras, the SMS-1, and an AVM-20. I can run dual sub outs on the AVM-20 if I need to, but I'm thinking I want to run a single sub out to the SMS and then use that to configure them both. Am I right? When working with 2 subs, do I set one up first by itself and then add the second? I'm trying to co-locate them for the SPL increase.

IMO you'd run a single cable from the LFE out to the SMS-1 input, then run sub cables to each sub from the SMS-1. Then configure as necessary, so you're right. That is how I did it in my room with my dual subs and SMS-1. I have the subs in different locations as opposed to co-located, but I don't think that matters as far as hooking it all up.