Cable pulling issue between floors

Trying to run a cat-5 cable from my router in my living room to my theater downstairs and I'm trying to figure out the cable pull. It is not a straight pull, it's up a wall, across a ceiling and through a floor.

In the same location there is a RG-6 cable that goes into my cable mode. So there is 1 wire already there, I just need to pull a second wire immediately next to it. Are there any tools out there to assist with this type of pull? I thought about pulling the existing RG-6 cable with a line attached to the other end, then affixing the CAT-5 to that same RG-6 cable and pulling back through via the line. I also thought about attaching my pull tool to the RG-6 cable with a lose zip tie and seeing if the attached zip tie will allow the pull tool to follow the patch of the existing wire making it possible to fish that way. My fear is if something goes wrong and I can't get that RG-6 cable back to the original location I'm screwed and now I have to relocate my entire networking system.

The house was built in the 70's and the guy that owned it before me was a DIY hack. The RG-6 cable on one end just goes through the carpet, it doesn't even have a wall plate. So I'm hoping like most things in the home he didn't affix the cable to the floor joists in the ceiling.

Any advice on a project like this? Is there anything on the market that can help this issue? Am I over thinking my solution?

I live in a split level, so everything is finished. I can't get to anything with out tearing up the dry wall.

I'm streaming 1080p mkv files with HD audio, so were talking 20gb files. I've got a ton of bandwidth and wireless just isn't enough