Your polish guy is right in that on high end audio system a cable upgrade can be just as significant in SQ improvement as a new amp or cartridge or other major component.
On lesser mid fi audio equipment it may not help and may not be perceptible at all.
No different than, random analogy, putting good quality real cheese on a McDonalds burger to replace that stuff that can’t even legally be called cheese, won’t really help the burger and the burger eater would not even like it.
You appear to have at least an entry level high end system (I have not heard the speakers you have) and you will get benefit from a cable upgrade to a point. I would not go for expensive cables but mid level kimber kable or Cardas or audioquest or any of the other high end reputable brands.