Hi,
I've used numerous HDMI cables with my G91 and never had any issue with video quality. From that I'm surmising that the G91 is not cable sensitive. I could check the video/scaler settings I have on mine if you think that would help you compare settings.
I do use mine through a 421 switch into projector now but previously have used it direct into the TV and then direct into the projector.
The video possibly looks like it's not synced. Do you have/have you tried another HDMI source into the TV? Is that OK ? Can you try the G91 HDMI into another display?
If you could tell me your video scaler settings that would be great. Thanks. I have tried it on 2 tv's and a projector with a HDMI over cat6 extender. Still the exact same on all sources.