First thing I would suggest is to work on your room acoustics. It's the single most important investment you can make for the money - if the room isn't right, you'll never hear what your gear can really do. Take a little time and learn about some of the issues on improving room acoustics, then either buy or make some DIY treatments. There's a lot of good information out there including the Room Acoustics Forum on Audio Asylum, Rives Audio web site, and Ethen Winer's site.
A basic starting point would likely include corner bass traps and absorbers for the first reflection points. I've made a number of custom bass traps and absorbers based on information available on the web and the improvement in the sound has been significant.
