As a former owner of a SMS-1, my advice would be: sell the SMS-1 and get a miniDSP 2x4 HD. With the miniDSP 2x4 HD you can have 4 independent subwoofers and won't need to upgrade your receiver as you can time align the subwoofers in the miniDSP, EQ them, then show the pair of FV15HPs as one mono subwoofer to your Yamaha receiver. That is the way I do with my three subwoofers, even having a Denon X6500H with Audyssey XT32 + SubEQ HT.