I moved from one good REL B1 to three total and then four subs (all set 60 or lower) and when set up properly I do enjoy it more, like most.
If one can 'hear' and localize deep bass I might suggest the overtones or a second order sub crossover getting in the way. I believe something is heard, not the deep stuff though. The four subs I have are not set so loud or set so high as to ever know where they are for me.
The 'air' and additional horsepower are nice additions. Good luck and good idea on trying out the SVS SB-2000 as a test (I have two of those and an SB-3000).