If you really wanna use treatment to affected low bass(quite a bad idea if you're not literally building a studio IMO) I think you're likely better off using frequency tuned membrane traps or
active absorbers instead of padding your whole room with 16" of rockwool. That said it'd be interesting to do comparisons of all these techniques, I still don't see what the benefit is supposed to be over multi-sub.
Obviously you do need some absorption to get reverb times down but that's very little compared to trying to "bass trap" your way out of room modes.
I'm becoming increasingly suspicious of claims you only need one sub as long as you're only optimizing 1 listening position. It would be interesting to measure a variety of rooms, but in my room the response is *quite* different in the same chair between leaning forward, sitting straight, and reclining. And I can't imagine being restricted to one specific position while sitting -- that's comfortable or relaxing. Head in a vice indeed.
It wasn't really possible to fix all those positions with just 1 sub and EQ. 2 made it a lot easier. And I don't understand the argument that 1 can sometimes make things worse. Maybe those people just aren't familiar with proper multi-sub optimization techniques, but I don't think it's mathematically possible for 2 properly optimized subs to produce a worse response than 1 under ANY circumstances.