Then the cause pretty narrowed to the DPP LNBF. I would try to substitute it by the same model , can you borrow it ?
I think I might try that next. I just tried adding a DishPro adapter (I figured I should probably have an extra one lying around anyways) but I got the same results. The next step is to assume I have really crappy coax strung in this (fairly new) house. I'm gonna run a nice short piece of brand new RG6 through the window and go from there. After that, it's a new LNBF. Thanks again!
You may want to try a Legacy twin or quad. If you need one, I might be able to help you out.