What kbps are your mp3's as mp3 is usually not up to cd quality and it would be a faulse economy investing in better kit as you'd not reap the benefits using mp3 imo.
A speaker upgrade to the B&W's would be a major step in the right direction though offering more depth and detail over your cheaper speakers.
I recently sold my arcam CD72t cd player for £220 which is about the going rate and would give you good results on a limited budget.
If your looking to upgrade your av amp I'd suggest you audition the usual suspects and make sure the one you choose has pre-outs. You'd be able to use an integrated amp to drive the Fronts for improved stereo and utilise the av speakers for music as well as movies (less speakers to worry about)

If you have a budget in mind let us know and we should be able to point you in the direction of some suitably priced products.

__________________