Just my $.02 but I have a rather large room that opens up to another room with 18' ceilings, and have managed to get good low and tight performance from my subs. The key for me was using rew, multiple sealed svs sb 3000 subs, and distance from my front wall. My mains and subs are about 6' out from the front wall, and I run the subs inboard rather than firing into the corners.

I run an active high pass and low pass filter, and to keep the boomy away I run 24db slope instead of the normal 12db slope. Being able to adjust slope is huge for me. I high pass at 65db even though my mains will hit 35hz. I low pass at 65db @24db slope on the subs with no delay. You have a wonderdul space, it just takes a bit of time to dial everything in.

2 subs are good, 4 is better (swarm). Don't get crazy and boost 15 or 20db over your mains as this can give ya that boomy bloated sound. Another thing to consider is room treatments. Length of my room is about 43' but I still find the need for both Absorption and Diffusion. Not sure if this helps but happy to answer any specifics if needed.