try a pair of vmps larger subs. paired w/a pair of used solid-state bridged amps & a good electronic x-over (like marchand, for example), these will give you clean accurate powerful bass at *way* less the cost than anything comparable. i'm a cheapskate, & this is one of the few products i bought new - still a bargain! how about down to 17hz, w/less than 0.5% thd at 95db, & less than 5% thd at 120db? and that's w/just one sub. regardless of brand, get a pair for proper 2-channel audio.
the above is yust my opinion, ymmv...