You want to improve Stereo sound.

You have nice speakers.

Everyone loves to say "buy new speakers!" but in all honesty the sound can be improved to get the most out of your speakers rather easily.

First I'd look at the source. You never mentioned what you source is. You likely could buy a really nice CD player and improve your sound.

You could buy some Audio-Tech Feet of Silence and improve your sound (seriously, of all the changes I've made in the last 5 year, Audio-Techs' Rack Of Silence, Discs of Silence, and Feet of Silence made the LARGEST difference and most notable).

You could jump right to speakers but I think you have nice speakers to begin with. Find out where in the chain is the weakest link and look to improve it.

CD player/DVD player, Pre-Amp, Receiver, AMP, Speaker Cable, Interconnects, the Audio-Tech stuff, any of those could audibly increase the performance of your system.