^^^Your problem is exactly what happens when the room acoustics are bad. It's easier to blame the subs, but it's the room, not the subs. I used to have the problems you describe.
Basically what happens is you have very uneven response in the room, and probably really bad right at the listening position, so when something like a certain song has bass centered at the null, you try to crank up the sub, only to make the already present peaks even louder. Or other times, a song may have bass centered at one of the peaks, and then the sub sounds way too loud. It's the room, because I don't have that problem any more now that it has been corrected at the listening position. It's a night and day difference that I can't stress enough.