Since you are already have a lot of toys including measuring mic, I'd try to experiment with placement and measurements. Only after getting good results with 2.0 I'd add up subwoofer(s).
Distortion at your screenshot below 200 Hz is very weird, because if UMIK is calibrated, such level of distortion can't be induced by amp or speakers at this SPL.
I'd investigate your room with stethoscope, because first idea is something rattling, like plasterboard walls or something else.
If you need fast result, hire the acoustician.
If you need more hobby style, first add up required furniture and absorbers/diffusers later. Maybe some thick motorised curtain over your TV.