Welcome!
I have a similarly sized/shaped room, not so elaborately built, nice! I tell others that the point of the insulation is to lower the noise floor so a greater dynamic range can be enjoyed. Also have treatments (10 GIK 244 panels plus 3 randomly filled bookcases).
Recommend reading Floyd Toole's "Sound Reproduction" 3rd edition to gain an understanding of how speakers behave in-room. It is the seminal work for audiophiles. Most importantly for you is the importance of distributed bass (3 or 4 subs, placed in the corners) to help control the 20+ dB bass peaks/dips that are inherent to residentially sized rooms. Currently use (3) 10" subs in such a setup. Other resources that promote a "swarm" of subwoofers are Earl Geddes (retired acoustician) and Duke LeJeune (owner of Audio Kinesis here at Audio Circle). Toole worked for the Canadian Research Council (promoted Canadian audio) for decades before retiring from Harmon International (home of Revel, JBL, etc.) and is very well respected.
As far as subwoofer design, most audiophiles prefer sealed over ported designs as faster with less overhang. Had transmission line (TL) bass 40 years ago - fantastic (deep, strong, very musical) but they were passive (8" woofer in 6 cu. ft. cabinets I built) and as such were too powerful for any room I'd ever be able to afford. Sounded magnificent in a 20,000 cu. ft. 160 seat chapel driven by a 20 wpc NAD 3020. Currently own floor standing TL main speakers that use a single (remarkable) driver ala Martin King's MathCAD application. Suggest learning it and searching for appropriate 6" woofers. Don't know what size the cabinet would be, but guess around 3 cu. ft. With 3 or 4 subs reaching deep, not ultimate output would be the goal.
