Though I've seen you on several threads, I'm not sure if REW is one of them. If you don't have measurements, then you should start there.
If you have only one seating position that matters (as is the case in my house, where my wife couldn't care less), then only one sub would probably be okay. I have 2 15's aimed right at me, supporting the TV. Looks good, works well, measures fine.
I also have ButtKickers under my chair. If you look carefully, you can tell that that part of the sectional is about an inch higher than the rest, but you wouldn't notice if you're not looking for it; probably depends on your furniture. The BK system I bought has a wireless adapter, but I didn't play with it much since I already had a cable run, so I can't tell you how well it works (though wiring is not a problem for you either, it appears). That said, I know my BKs only start "kicking" below mid-40sHz, and have never responded to voices. As with most things, you can overdo it, but I have found a setting that works well for most things. I've heard there are better systems out there, but this was a good bang for the buck/butt (I like that one!).
That said, I have an Ultimax 10 kit waiting for me to assemble to put right behind my chair. So I'll (eventually) be able to let you know if a nearfield sub makes much of a difference. And I'll be able to measure the difference with REW and VibSensor, which should also be interesting.
Yes, we're all crazy on this bus.