#1: You have either WOW or Warner, upgrading your DVR to a Scientific Atlanta 8300 HD DVR will allow you to have HDMI out.
#2: Why the heck are you running RCA out from your 8000 DVR? Either buy an optical cable and use the optical out on the box, OR use a single RCA connector, but connected it to the digital coax out from the box to the digi coax in on the stereo receivor. This way you'll actually get your 5.1 surround.
#3: If you do get an 8300 HD DVR, you can run your HDMI 2 ways. If your TV has 2 HDMI inputs, you could run each individually to it, then an optical cable back from the TV to the receivor. If your receivor does HDMI switching AND is HDCP compatiable, you can run both HDMI cables to it, and a single HDMI cable to your TV.