Add a subwoofer to Von Schweikert 4Srs?

I'm currently using VS 4Srs after upgrading from 4 Jrs late last year. They are (finally) getting broken in and really singing. No complaints except I'm longing for a little more low end. I'll admit it...I'm a bassaholic but I don't like that home-theatre-low-rumble without a cause sound. Never owned a sub. Any recommendations (besides seeing a therapist)? The best woofer I have heard to date and would proud to have in my system was a Talon I herad at last October's RMAF. My appreciation in advance.