Just me personally, but if I couldn't go over $400 to get the excellent Monolith THX Select 10 for $500, I would have bought two of the JBL 550p sealed subs for $190/each. The 550p is a great sub for the money and it's sealed design is tailor made for medium to smaller sized rooms.
Subs>RBH I-12e/I-12. HSU VTF-15H mk2. Monolith THX 12(x2)/THX 10(x2). XTZ 1X12. SVS PB-1000(x2). Speakers>JBL 270/235c/230/225c, Arena 130/125c. Jamo S807/S803. Infinity P363/163. Sony CS3/CS8/CS5. QA 3020i/3090Ci, 2020i/2000c. Monolith Cinema 5 bs. Polk RTiA1/CsiA4. Other Audio>Sony MDR-Z7m2, WH-XB700, XB32, XB31. Sennheiser HD58X, HD4.50, PC37X. SIVGA SV004. HyperX Cloud PS4 HS. Plantronics RIG500 Pro HS. LG FH6,RK8,RK7,PK5. UE Boom3.