Yeah.. that's the biggest downside of PLEX.. that no direct integration in that way.
At least from MY understanding... MOST of what they would be watching/recording from OTA, would be recorded for later.. so in the end, not the END of the world if recorded, drop the file, PLEX builds the listing for it, and then they watch it.
The few live things.. might run into a bit more of an issue.
Though.. they always do have the option.. of a direct cable connection INTO the TV then as well.
One of the, is boardline 'anti windows'.. so introducing WMC might not be the BEST choice.
At least with plex, can do a Linux (or NAS based) server solution, and direct to TV app front ends, Roku, etc.. without necessarily getting windows involved. Even just as a server, they might be OK with it.
It LOOKS like HDhomerun has Linux/mac software anyways.
Rogers Ignite Xi6, LG 47LV5400 LED TV, Yamaha