Have been asked by my parents for help, but not super sure on this particular topic / option myself. 

Basically they have a projector in there lounge and rest of system like amp, mysky, Dvd player in other room. 

System currently cant do HD as its running over what looks like RCA cables into back of projector. 

They want a to get HD content to projector but cant re wire for HDMI cable. Was suggested they do HDMI over coax to get HD to projector and TV. 

Is this a good option? Will this actually give a good result, for mysky HD and Blu-ray will HDMI over coax balun.