Are you asking if you can? or are you offering this as a suggestion?
You should be able to use a HDMI splitter, but make sure it still carries audio. My Pioneer 1016 amp had HDMI, but does not carry audio on it, strickly video. so I'd have to add the splitter before the amp.
What HD sources are you using? If it's SAT, it may be easy and cheap to pick up another receiver off ebay (I picked up several myself), but you need to run seperate coax from the dish to the set top box, as the HD signal does not like to get split.
If you're using dvd, hd dvd or blu ray, the player may have 2 outputs, one of which may be component (3 RCA cables, or labelled as YPbPr) which will give you up to 1080i, which could be routed to the second set. Again, this is only video, and you'll still need to get audio there.