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

I agree with @oddiofyl that a good preamp is of paramount importance and a hard thing to get right. Simple tube circuits are the best solution I've found personally.

My amp has a non-working left channel...sent it back to the factory to have a look see and fix.   I looked around the room and noticed the expensive power cord for the amp was lying on the floor not doing anything.  Stupid 82 old me replaced the "upgraded" cord on the CD player with the expensive one that used to drive the amp and was bewitched by the improvement.....just ordered new power cables for the rest of the system. 

The preamp is nearly as critical to the sound of your system as the speakers.

Common audiophile wisdom - active preamplifier is extremely important.

Speaker cables, like everything else, are important too. My speaker cables cost new or used as much as my speakers. Perhaps I overdid it a little but I haven't had to replace them in 25 years, and my system now sounds incomparably better than 25 years ago with the same speakers and cables. But it's a modest system, both speakers and speaker cables cost $1500 new 25 years ago.

Back in 1992 I purchased a AR SP-9. It made a huuge difference! It opened up the soundstage width, depth and detail. All improved immensely! It was though I walked into the room of the performance.