High definition distribution within home over coax?

With standard def TV I had four TiVos distributing their standard video signals throughout my house on coaxial channels 71, 73, 75, and 75. (Each TiVo controled with an IR distribution system).

I'm a convert to HDTV now (HR20's - God help me) and I have them feeding the same network (in standard def though), but it would be nice to be able to view HDTV from each HR20 on each of the other HDTV's in the house. This would require a way to split out HDMI data and convert to ATSC over-the-air signal to distribute over the coax. To date I have been unable to find something like this. So until the HR20 is upgrade to allow ethernet or WiFi distibution, has anyone found such a device to convert to OTA signal to distribute in the home over coax or any other solutions to this?

Thanks...