How can I figure out the surround sound system left behind by the previous owners?
If you simply used the ohm meter to check between the wire pair at each of the three terminus points then it is very likely that you would read infinite. The reason being is that the other ends of the pair are laying open someplace else. 

To check for the wire routing you would need to check for continuity from one wire at say point C0 to one of the wires at point F. 

The two pairs of wires at point F may have been connected to speakers located at or near that point. If that is the case then it is likely that all six of your speaker wires terminate at some location that you have not yet located. Some systems that people install put all the equipment out of site in a closet or adjacent room. This is particularly true for cases where the equipment is almost totally controlled through a user interface on the video screen.

You may have wire pairs looking something like this coming from a closet someplace:



You could investigate trying to trace the wire routing. There are tools that you can purchase that inject a signal into a wire from a battery operated transmitter. Then there is a separate receiver unit with a probe that you slide along the wall. The receiver module will produce a sound that chirps and varies in intensity depending upon how close to the driven wire it is located the probe. I own several of these units and have good to mixed results with them. Here is a link to the unit that I have had reasonable success using.

 

You can find this unit at better hardware stores, big box locations or online. The price showing at the link above is decidedly better than what I paid for the same unit about 10 years ago.