I just hooked up a video processor to my HS20 via HDMI and tried to set the VP's output to 1366x768, but I got the "signal out of range" message. Do I need to switch to DVI input for this, or is there a setting on the HS20 that I need to change to accept 1366x768?

TIA!

There are no settings you can adjust. You can try and force it via power strip but nothing inside the projector allows the setting.