nightout: Are you looking for more kick for a BASS or more "bass" for your system?
If it's more kick for a BASS, another option is to plug the bass into a Phil Jones Pure Sound Briefcase amp.
You can put a rechargeable 12V motorcycle battery into it which will run it for a "number of" hours - probably more than the 2 hours advertised for that discontinued ($700) Carvin Sub but probably NOT the 5-6 hours I get from S1s.
I have a Phil Jones Briefcase ($999 street price). It has great tone and there's a DI built in so you COULD run a cable to your S1 for a bit more sound level in the 100-1KhZ range. And you can use it as a great practice/small gig amp or as an onstage bass monitor that you plug into large sound system.