When using this card I only need to have one Coax cable connected?
I suspect that Mythtv and/or IVTV for that matter does nothing with
the FM connector which is most likely input 7. The TV coax connector
must be input 6.

I presume that internally there is a switch from one encoder to the next.
That must be how the IVTV driver is working.

So each tuner shares the one cable?

No support for FM capture yet, and you don't need to have anything connected to it or any other input you're not using.

Whoops, didn't catch the PVR 500 thing at first... Not sure about the connectors there. However having two tuners on one feed is perfectly reasonable, it's just a matter of having an internal splitter.

Yes, one single cable feeds both TV tuners on the PVR-500.

-brendan