Any real difference in RCA cables quality for sub?

If you are getting hum or noise, try a better cable.
If not, I doubt there will be a significant difference by changing cables.

Especially in audio, and especially on Audiogon, what is "significant" depends entirely on the listener. To me, "significant" means a bigger effect than moving the speakers or my listening chair by six inches, and by that definition, I'm confident the answer is "no."

If your system is quiet you have have good start. The signal needs to get to the consumer without picking up NOISE.

Hook up a sub and get a hiss from the tweeters. That noise..

I’ve also seen RCAs pass a signal BUT one end to the other it would lose a strong enough signal to make the sub respond correctly. Turn it up and it would work better. Correctly, I would question. Usually with copper as a clad OVER aluminum or simular conductive alloys. That type of IC is real common in Auto audio gear.

A good copper IC with good terminal ends. I usually solder BASS stuff and use gold clad over the terminals.. Just works great. Copper/gold for bass.. Peas and Carrots.. :-)

I use a weave works perfect.. 3 meters is about 30.00 usd with locking ends.. Copper/silver clad PTFE. or OCC PTFE. Cooking a bunch right now..

Regards

Cables do make a difference with subs, especially if you have a really good sub. But. The difference is  small.

OP a Spdif cable works fine especially for longer runs or multiple subs.  Save all the money you would spend on exotic metal conductors and fancy connectors where it can make a difference, a single ended line level interconnect.