I need to get my home theater to sound good with mp3s. Yes, I am aware that mp3s aren't good quality.
Im slowly upgrading the system, what should be replaced next?

I have a crappy $150 receiver, crappy 18 ga. cables..what should I replace first?

I have very nice speakers, Axiom M2i's for the fronts, VP100 for the center, and the EP175 sub. I'm waiting till I get the money for rears. I don't know what, but something sounds really bad on the system. It might be muddy bass or distorted sound. How can I isolate the weakness and fix it? It kind of sounds like the levels are messed up or something, but I have played with them tons. Maybe like the seperation between sub and mains isn't right...

Movies sound very good on the system, but the setup is lacking something musicly...

I really need some advice on what to do, thanks in advance.