Question regarding subwoofers

I have an RHLabs SB-1 that’s served me pretty well for many years and use with it with my Acoustat 1+1s. (Had it refoamed a couple years back.) As well as the 1+1s image, I’ve always been slightly annoyed by having a single subwoofer between the panels. When playing something with a large sonic image like orchestral music the setup works fine. However when playing something more intimate like Jazz it’s easy to "see" where the lower frequencies are coming from: The middle. As my listening has gotten more refined it’s getting to be less acceptable to me. So I’m looking possibly at a pair of smaller, powered subwoofers. Why powered? Simple: If I do this, I’d rather the ARC VS-110 just power the panels. So, my questions:

1) The SB-1 has a single 10 or 12" driver. I’ve seen subs anywhere from 8" to huge. What folks experiences been with a pair of 8-10" powered subwoofers? Too much? Not enough?
2) Did a pair of subs affect imaging much? IOW, could you discern enough left/right to make it worthwhile?
3) How tough was it to balance them?
4) Do I run another set of interconnects from my SP11? Or do I get a set of Y adapters to feed both subs and amp?

Let me close by saying that like with most things audio there’s going to be a lot of "it depends". I get it. But I’d still like to hear of folks’ experiences as I do see a lot of systems with subs.

As always, thank you much for your time and comments!