I have 3 receivers, 2 HD and SD.
One thing you could do would be to dump the SD receiver (save $5 a month) and run the new HD from one of your present HD receivers. I assume you are using HDMI cabling at the moment so run the new set off the component side.
Actually, it might be easier for you to run the new set off an extended HDMI cable and run the present HD set off the components.
Of course, you will not be able to watch 2 different programs at the same time.
This is how I solved my problem and saved $5 a month at the same time. When I cancelled my SD box, DTV did NOT give me ANY grief about it (I was only 1 month into a 24 month contract.) DTV sent me a prepaid shipping box so it didn't cost me a penny to return the SD box.
I'm using a IR extender (Radio Shack et al.) coupled with an $8 IR remote I bought on eBay. Works great for changing the channels from the other room (about 30' away from the HD receiver).
Longer HDMI and component cabling can be bought at monoprice.com for a very reasonable cost.