Here's an update:
I went ahead and cut the wire and it was in fact the left, right, & video wire going back to the stereo. I added plugs to the cut left and right wires and had enough cable to get them into the back of an rca coupler plate.
I replaced the single coax cable plate that was in there with a three way rca coupler plate. I didn't bother with the video (yellow) wire...I swapped that jack out for a coax coupler and connected the existing Wineguard antenna wire to it and put it all back together.
My problem now is that the Sony cdx f5000 stereo apparently won't accept an Aux input without another piece of equipment
(read about this in another thread). It has aux bus inputs on the back but I can't get it to work.
Anyway I have attached a pic of the finished product.
I am going to cut a small hole in the back corner of the bottom of the overhead storage cabinet to neatly run the wires down to the TV without having to come out of the front sliding door.
Also....I did find the other rca cable under the couch on the street side with the other sub wires...as suggested earlier in this thread.