Do speaker cables really make a difference ?

On this forum they do. On scientific forums they don't.

     Science loves me

         This I know

     'Cause my textbooks 

          Tell me so

        But my mind

    To my ears belongs

        They are right

  The books are wrong

   Yes: Science loves me

   Yes: Science loves me

             etc...

Confirmation bias is often cited by cable deniers, yet it's rarely acknowledged in the same post or thread that this interpretation goes both ways in terms of confirming one's previous beliefs - more like "rejection bias" for the cable deniers. 

Like almost everyone on this thread, my answer would be, very much, YES. But, as usual that answer means absolutely nothing unless you hear the difference yourself, and like what you hear.

It seems to me that the key issue for anyone in your situation (and mine) is to have a nice hi fi dealer who will lend you stuff so that you can make comparisons.

Confirmation bias is real and very common here.  Not saying cables don't matter but when two cables are close, 2 component are close, a new component is added that doesn't make much difference, tubes are swapped, it is easy to get confirmation bias.  

I am certain many of the positive reviews here on the forum absolutely reek with confirmation bias. 

So do your tests for several hours each.  Keep an open mind.  go back and forth a couple of times.  Do everything you can to keep from being a victim of confirmation bias.

Sometimes I just do the upgrade and don't try to judge it, other than to confirm I did no harm.  

Jerry