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

Right now I'm using 2 identical Anthem power amps MCA 225, NAD C379 preamp, Cambridge audio cxn100, and a Marantz single cd player as a transport using the dac inside the NAD. As far as speaker cable I'm using some that I found on Amazon and it seems to get the job done, the name of this speaker cable is WBC.

One of the most  significant jumps forward in sound quality in my system occurred  when I made a substantial upgrade in the preamp. The only thing that made as much difference was room treatments. Like most of this stuff, it’s probably system dependent, and others may have had a different experience

I went from a Rogue Audio RP-1 to an RP-7–almost triple the price, and it made a marked improvement.  As for speaker cables, I was a bit of a skeptic, figuring that “decent” cables in the $100 to $300 range should be enough.  However, I purchased a set of Silversmith Fidelium speaker cables and was astounded by the improvement in sound quality.  My non-audiophile wife even commented on the “major improvement.”  So, quality cables do make a difference.  In both cases, however, keep in mind the law of diminishing returns. Will a $50,000 set of “Cattywumpus Delight Mastercables” be 50 times better than the Fidelium?  Not likely at all.  Ten times?  Not likely, as well.  Figure out what you are willing to spend, and then do some research and try out a few ifdealers will permit a test—I the the Cable Company has a trial library.  Specific cables may sound different in different systems.  Others may disagree, but my experience says cables do make some difference.

You know, some seemingly small changes can make a big difference...I believe we should first work from the source outward.  For example, get the speaker cables off the carpet!  Can make a big difference, a whole upgrade!  Then get revealing interconnects, to me musical, revealing but not harsh ... Speaker cables...buy used! Same for Interconnects... can get excellent  values for outstanding sonics..  Then, I'd focus on the speakers as they have the ability to assign the sound, music characteristics you most appreciate...certainly, there are certain synergies between some speakers and electronics...but I've found that if you get the speakers right and the foundational basics "right" you may be surprised how good your current pieces work...or at the least you know what the new candidate brings to the equation.  IMHO, we too often forsake musicality for a "different" sound.  To me, music is an art, not so much a science...I'm a romantic!

My local hifi store brought up a good point; they said that the only thing between your amp and your speakers are the cable.

Absolutely, but talk is cheap. Don’t believe anything or anybody, just listen yourself and make your own decisions. Has the dealer not done a demonstration for you, comparing what improvements can be had by moving up the speaker cable ladder? Same goes for pre-amps. It is always nice to know what is possible, even if you can’t afford it today.

I think the question you should be asking is what is the weakest link in your system. I don’t know what your NAD pre- section/DAC or WBC speaker cables sound like, but maybe you should be upgrading the DAC first? And even before that: Are you using the manufacturer’s interconnects that came with the equipment? That would be the first place to upgrade- the best speaker cables or preamp in the world won’t make up or re-generate the details lost by poor interconnects or an inferior source upstream.