So I made sure that all the options on my receiver was giving all the bass to the front speakers and ran some tests, and from what I could tell the amp would just stop driving the bass at about 100hz so that there's this moment of chest thumping bass, and then the note gets lower and it just, poof, gets quiet. Greg did some research and found out this is a flaw in our recevier, which lends weight that even a bad subwoofer might help. Though running the tests brought back fond memories of those speakers unscreen saving computers and blowing grocery bags around. We'd love a receiver that does component and have for a while, but I'm not sure the information on how well a receiver would drive my speakers is out there. Modern systems are all about the tiny little speakers and the subwoofer working together, not about older speakers that could kick most subwoofer's asses. I'm also worried that since they're relying on a powered subwoofer they just don't amp the bass signals below a certain frequency, expecting the subwoofer to take that extra burden.
So, that's my current thoughts.
Oh, I even thought about mounting a larger woofer under the floor, but I don't think that will work either.