I have never done that but my brain tells me to put TC between extension tube and the lens. However, the Pentax TC manual mentions they were not designed for macro works.
I second that. The TC (I have MC) I think is/was? constructed specially for the lens to be attached right to it. So first comes the body, then tubes, then converter(s), then lens...
I also have no experience with such kind of set up but I guess I'd try it some day as I do have MC and tubes.
Thanks.
Boris
