that would be the bodies, even though 3Hz seems too low, it is worth it. A difference can certainly be heard from the regular cmc6 bodies, esp when using the 41 caps, which tend to have capture less bass than other caps. You do have to watch for air conditioning rumble or ceiling fans blowing air on the caps. It shows up much worse than on regualr cmc6's.
On the low Hz caps , I have never ordered any, but I know someone who has, some years ago. I actually use these "special" 41 caps occasionally and seems to my ears their is a difference in the low end.
I have never done a comparison though. I'd like to.