I use a REL T5 8" downfiring sub. Musical Fidelity M6si integrated and Neat Xplorer speakers. Small sub fills in the room nicely. 22' deep, 16' wide and 10-11' ceilings.
Speakers 7' apart and 18" from front wall, chair 8' from speakers. Sub positioned at 10:00 against left wall and about 18- 24" ahead of speakers.
For a small sub in works really for my room. I was looking at upgrading to the Signature SE so your posts caught my attention. Surprised about bass lacking. Also surprised Legacy stated no burn-in time. Watching w/ interest...