I have the 622 hooked to a hdtv downstairs and a sdtv upstairs. If I had a HDTV upstairs, would I see hd signal if the receiver was in single mode instead of dual?
Not by using TV2's outputs. They are limited to RF and composite and HD doesn't pass over those. You could run component or HDMI (depending what you use for TV1) to the upstairs TV though.