I also use an iScan Duo. While I get an image with 240 x4, it will blank out after some time. These are the only settings that stay consistent:
You’ll want to hunt down the latest firmware too.
Also, if you’re using a NES or SNES, set those output modes to DVI and route the audio out through the 3.5 mm jack to the DVDO. If you don’t you’ll get weird glitches.