Looks like you have a solid choice of gear there.
Like many of us, you don't have a dedicated space, and limited to getting the most out of a living area-more importantly BOSS approval.
I'd try placing one behind the listening if possible.
Trust your ears.
I have 2 RELs- both of which are behind the listening sofa. Very convincing and no unsightly additional boxes cluttering up the area.
"Based on the reading that I have done, I understand that the subwoofers should be placed alongside / parallel to the main speakers, and not behind them. "
REL training w/John Hunter I attended had them behind the speakers. The corner of the room was used as starting point and pulled out. Also, the main speakers weren't necessarily equi distant in positioning.
Final positioning would look odd, but sound great.
Speaker positioning was treated like focusing binoculars. No lasers, tape measure, DSP.
My 2 REL's are behind the listening sofa alongside the side walls.