What to add to my system for best sound?

Howdy,

I'm new here, and learning fast, but oh so much to learn. I recently bought my first real stereo (don't laugh) which consists of very basic stuff, and I'm realizing after listening to it that I have more expensive tastes than this stuff can handle. I have Axiom M50 floor standing speakers which are decent, balanced, dynamic, but lack detail. They are powered by an Onkyo receiver and cd changer. I want to add something to get the best sound out of this stuff (I'm going to get some better cables to start), but I'm very curious about the whole "tube amp" thing, and integrated amps and pre-amps.

I'm prepared to buy some used stuff to make this sound better -- especially the detail issue I mentioned -- I want the sound to draw me in more. I might even buy more speakers, and just use these Axioms somewhere else...

I can spend up to $1000 on more stuff (used stuff bought on audiogon probably), if Santa is kind to me!

Thanks!

Julie