Will a high quality preamp really make a difference in sound?? Also speaker cable

Put world class preamp in any decent system and you will probably agree with me. It is a transformative experience.   Makes the whole system sound better and live up to its full potential 

There are many great speakers out there hobbled by a mediocre preamp.  Or a so so amp.    Lots....  Part of the reason we've all been chasing better sound.  

 I think spending as much or more on amplification than speakers yields great results.  

I think the preamp is the most important component in the chain.   I usually spend over budget when I replace a pre so as not to make a lateral move.  

Unless you've had a world class preamp swapped into an already good system. It's hard to explain how pronounced of a difference it CAN be.  May take trying a few but a great one can really elevate your system to a different level.