I'm coming in a bit late, but I definitely agree with the others above about skipping the McIntosh processors and amps, and going with the SVS subs to get substantial savings.
SF Venere family all the way around: S, 2.0 and Center. Coming off Paradigm Studio 80s, 20s, C with Servo 15 that I thought sounded muddy.
You didn't say whether you have already purchased the Sonus Faber speakers, but another way you can save money is by compromising on the rear channel speakers. However, do not compromise on the front three speakers. I don't know how much you might save by doing that, compared to the substantial savings you will get on the processors, amps, and subs.
Room is a 20x20x20 living room with large openings on two walls - not dedicated HT. The lack of impact from the Servo 15 is my main reason for considering 2 subs. My thought was that I'd use the front sub while listening just to music and turn on the second in the back of the room for movies.
The very long wavelengths of bass sound reflect off of walls, ceilings, and floors and interact in a major way with the primary sounds coming directly from the speakers. These interactions can create additions and cancellations that may appear in your listening room in fixed standing patterns, called standing waves or troughs. You can locate where these standing patterns are in your room and adjust where you place the sub woofer and/or your listening position to avoid listening where the standing troughs are located. If you're lucky, these positions are practical. More often, however, they require awkward furniture arrangements or are impractical.
The main benefit from using two subs instead of one is not the extra loudness you get. If placed in different locations, each sub will generate a different set of standing waves and troughs. Their placement will complement each other's sound. In that sense, you might do better with two smaller (12") subs in different locations, than with one larger sub.
