I did some research. You cannot use a splitter, it has to be a modulator. A modulator is powered from the receiver and has to be the correct type for your system. But it does look like my dish is able to have a third coax connection
I got an RF modulator to convert component cables to coax. It works but my office TV has waves showing. The ATI TV card will only display B&W images

So I know it is a week signal vs. the signal from the old receiver output. I put a coax signal amp in the line but nothing improved. So I'm unable to record TV to my PC, unless I want B&W. I've been putting the UFC and WEC fights on DVDs for a son of mine that does not have the channels.