I connected my Mac Mini to HDMI-2 of my DVDO iScan Duo, but when I select the HDMI-2 output the screen is blank. The output of HDMI-1, connected to a DirecTV HD-DVR, works fine, and the Mac Mini connected directly to the TV via HDMI also works fine. Does the iScan Duo not pass output from a computer?
Don't know a thing about the DVDO, but I think you're running up against the same issues that affect Mac mini owners trying to route their HDMI through certain brands of AVR...the Mini may not recognize it's properly connected to a display or if it does, it may not retain EDID after you switch away.
There are devices which fool the Mini into thinking it's still connected to a display, you'll have to decide whether that extra expense is worth it.
Which Mac Mini do you have? I have the current "server" version, with the HDMI and Mini Display Port outputs, and an iScan Duo. I believe I have done what you are trying to do. I can verify in the next day or two.