I've found the optimal room location for the main Speakers ability present a sound stage is usually not one of the rooms optimal bass modes.There are simply too many room and system variables as well as your personal taste.
Map your rooms bass modes using the crawl test standing up. Then order some long XLR or RCA interconnect form Blue Jeans or Mono Price.
If your in the U.S. SVS Subwoofers offer what seems to be a simply painless trial period.
I believe their products provide a functional amount of remote equalization, optimization, and gain along with three customizable memory presets that might better match your main speakers low frequency presentation.
Subwoofer single processing is vastly different and typically limiting. Best of luck with it.