I have a Mitsi 48413 (does not have the HD tuner) and I have my 811 installed via the DTV Component port. I also have it hooked up through DVI as well.
First off, you will need to hook up the 811 through S-Video or the components and go into the main menu and change the output from 720P to either 480P or 1080i. The 811 comes set to 720p by default. Your Mits can not do 720p, so it either needs to be set to 480i, 480p, or 1080i. Once you have this set, hook the 811 up via the component cables or through DVI. You will need a DVI-D cable for this. They can be bought on the web or on e-bay for as little as a couple of dollars.
-Mark