I am running all of my video through the 990, and with an MX-500 you should be able to set it up so that things run pretty smoothly. Does your HDTV have a DVI or HDMI source, and if so do any of your sources include a DVI or HDMI output? If either of the answers is "no" then you can make things very simple: just run all of the video cables to the 990 and run a component video cable from the 990's monitor output to the HDTV. The Tivo would have either component or s-video output (preferably component if it's available) and a digital audio cable (optical or coaxial) to the 990, the VCR would have composite video and analog audio, the DVD would have component video and digital audio, the Zenith's OTA tuner would have a digital audio cable (since the video signal is produced in the TV, there's no video cable to worry about), and you might need to run analog audio from the Zenith for the other over-the-air (I'm assuming that antenna 2 is analog TV broadcasts) since it may not output the audio from the analog tuner to the digital audio output.