In theory one sub should be able to be used to optimize bass for a single listening position. However, multiple bass sources seem to be the favored way to go in asymmetrical listening rooms to better deal with modal peaks and nulls. So, as the owner of 2 Rythmik F15 subs, I've seen first hand the effect of a single sub and the benefit of adding a second one to improve the bass response and it's what I'd recommend.
I'd suggest running your mains full range to have 2 more bass sources to add to your sub sources.
Another thing I found incredibly helpful was an acoustical measurement tool to "see" what my ears are hearing. I use the Dayton Audio OmniMic but there are others like XYZ and REW. I charted 99 candidate sub location combinations in 2 hours so that I could then analyze the results and pick the "best" location. Do you have a measurement tool?
While you didn't mention it in your post, do you have bass traps and parametric EQ available to you to help optimize the bass, regardless of which sub(s) you buy?