Which wire has biggest impact?/

The Poynting vectors don’t travel in the wire, silly. By the way, your auto spell check appears to have blown itself up. 

@bopper
off topic but I know a guy that goes by the nickname bopper.  Do you happen to play trumpet?  Does the name Crossmen mean something to you? 

If not, pardon the interruption.
if so, we know each other.

cheers,
Bruce

Millercarbon got it right - whichever one is the worst. 

If they're all the same, I'd start with the interconnect between the source and the preamp, then the preamp to poweramp, then speaker cable. 

i agree with @millercarbon.your system is as good as the weakest link in the system.find the weakest link or component and upgrade it suitably.