I recently upgraded my sub to the HSU VTF-2 MK3 which I highly recommend. You can change the tuning characteristics of it, and its a monster that is a true value. My friend also has a SVS PB10, and it is an amazing sub, especially considering the cost and that it is a 10" driver. Both muscial, both can go very low (~18 HZ clean), both can be had with shipping included under $600

M60, VP150, QS8, HSU VTF2-MK 3, Marantz SR8002, Oppo BDP-83SE, 50" Panasonic Plasma