Is 35’ and 50’ to long for RCA sub cables?

Again is it noisy?

Again is it noisy?

Regards 

Regards

I’ve been told to run XLR (mic) cable and then just use the two conductors instead of all three for RCA. Would that help even though my subs don’t have XLR inputs?

No. You’re still putting a single ended signal down the cable. In order for common mode rejection to work, you need two signal wires, each out of phase to the other. 

Use RCA cables and see what It sounds like. More than likely it will be more than good enough for a sub.

I am running a 75 foot subwoofer cable to the home theater subs and no issues. Make sure they are shielded. I bought mine from Blue Jean cables. Also, Mediabridge makes a decent shielded subwoofer cable and you can  those virtually next day service with Amazon Prime. 

Why not go wireless?

@OP,
You are between a rock and a hard place.
I would take @audioquest4life 's rec and get a good shielded sub woofer cable in RCA. I know Audioquest makes some inexpensive sub cables that include a grounding wire-which should minimize any ground loop hum.
Bob