Open Floor Plan Listening Room

Excellent, thank you.  Funny you should mention Acoustic Frontiers.  That’s who I reached out to for a quote in order to handle the work of calibrating and positioning my subs and speakers.  They are local to me so if the consultation price is right that’ll work out really well.

You might be sitting in a NULL spot. I use the 1/3 speaker setup and have used the 1/5 setup in the past. This means placing the speakers 1/3 of the room length from the rear wall and my listening position is also 1/3 from the wall behind. Since you are hearing a lot of bass 45 ft away, I would try using different speakers and listening positions in your room. Check out speaker room setup from the likes of Cardas and others

an open floor plan shouldn't really have a null spot

But what if it does? The description seems to be exactly a null, which could indeed be the case if the listening position is halfway the length of the room. But it could be that the louder bass elsewhere is actually a peak. So as I said at the beginning, measurement should come first. The only investment is that of a $75 calibrated measurement microphone.

You need an additional opinion like a hole in the head but I have exactly the opposite problem. My audio room is really confined (8-1/2 x 12-1/2) and uses not only room treatment but multi band equalizers to null out or correct (mostly) bass... so count your blessings! I’d trade in a minute if I could.

The problem with movable walls is that they tend to resonate more than fixed ones that can be re-fortified for rigidity. Back in the day I had my share of planar speakers (Magnepans, Quads, etc.), all crying for more bass. My suggestion along with others here is a subwoofer but without any ports (or block the port) and a very low crossover point, judiciously used and keep your room open. Good luck with your choice!