IMO, since you seem to be gainfully employed, I would put some money under your mattress every chance you get, and save it up until you can buy something more capable. What’s going to happen, is once you can hit your spl goals, your going to seek extension. I also recall that you enjoy movies, and as such, I think your selling yourself short by dismissing the 25hz and lower region. I also would disqualify-10db at 18hz useable. You mentioned 4 sub1000’s as an option. That’s roughly 500bucks. I think it’s 500 bucks you should save and invest in better subwoofage.