You don't need Letscan to use image grabber. Search the forum for how to use image grabber on it's own.
Letscan does of course make it much easier.
The Canon live view is a low resolution (Canon 600D: 1056x704 pixels) , but still ok and a good place to start learning/using David (especially if you have the camera).
I have chosen a different route, after starting with Canon cameras. I now capture FullHD with a HDMI capture device using the Panasonic GH4, but this is not an option for Canon cameras except the 5D MarkIII.
Why do you say that the Canon 80D does not work with David (live view resolution is low: 960x640 pixel) ? Maybe you need to upgrade the Canon DLL ?
Panasonic GH4 4K with lens 12-35, Inogeni 4K to USB3 hdmi capture device, projectors: Acer K135/Acer K11/NEC V260X, Canon 60D, macro 60 mm, MagicLantern