I always argue that speakers make the greatest difference in sound. That does not mean that you should go right out and buy new reproducers. You need to discover within yourself the kind of sound that you like. Do you want a warm, enveloping sound (heirs to the "West Coast" sound of our forebears) or something cool and reflective ("BBC monitor" sound) or something analytical and ultra-precise. I'm overgeneralizing madly, as someone will doubtless remind me, but I hope you get the idea.
My point is that the speaker, more than any other component, will establish the foundation for the kind of sound you like. Having set that cornerstone, you then choose electronic components consistent with your overall sonic goal. There's no magic to this synergy business, simply a clever and careful matching of the strong points of each link in the signal chain to yield an overall consistent endpoint without concatenating so many weak points that you have unacceptable defects in the finished product.
Listen, listen, listen. Not only to everybody's system you can get access to but also to as much live music as possible. Define your own tastes. Figure out how much you can spend. Buy what you like. Enjoy.
will