Is there a difference in sound between a coax cable and an optical one?

It's not the RCA cable that's a problem.  It's the RCA jack on the DAC.  On many RCA jacks inside, there is a pressure plate which the pin/tip of the RCA plug touches to make contact.  Over time, if there is tension on the cable, it will bend this pressure plate away and eventually there will not be contact between the pressure plate and the RCA tip.  You really won't be able to see this just be looking behind the components.  It is actually inside the RCA jack.

AUX,  10-4.  Got it.  And thanks again!

You could always support the rca with a small piece of foam or other neutral material so that the rca stays level with the input.🙂

Tom:  I like that idea.    I'll have to do something.  It's annoying to not get any sound out after you set yourself up with the music and some "suck down" and then..... ZEEEEERO.  Now i have to get up and wiggle and jiggle the cable.  Thanks!

shtinkydog, nobody can answer that, since it is system dependent.  Optical should be better, because it does nor create ground loops and is not sensitive to any electrical ambient noise, but on it is very susceptible to a system noise. System noise, on either makes threshold point variable - not only in amplitude but also in time.  Uncertainty in time is jitter.  Jitter is noise. Going to coax helps, because transitions are 10x faster, but fast transitions create standing waves in the cable (reflections) that alter timing.  Nobody can tell you what is better.  They can tell you only what worked better in THEIR SYSTEM.  You have to try for yourself.