Sepulnation

Hi, I have following setup: Front: Klipsch R-820F Center: Klipsch R-52C Back: Klipsch R-51M SW: Klipsch R‑120SW controled by receiver: Yamaha RX-A3030 and I have feeling, that in lower volume is everything fine, but in higher volume the subwoofer does not have enough power to play with R-820F. How to solve this problem? I wanted to buy another SW Klipsch R‑120SW, but i am not sure, that this solution solve the problem. I am looking for brutal bassing. Question is: two subwoofers equal more bass and power or not? Thank you. Honza