What is it that you are displeased with right now. I am no fan of receivers but are inexpensive integrateds going to make a huge improvement? Perhaps not so much to spend the cash. Preamps are more important for sound quality so adding a power amp while important not so much for your speakers I believe.

I'd look at your source - speaker positioning room acoustics. Certainly a better amp will help but I would look at used higher end amps - Sugden, Naim etc. And I would also consider avoiding the amp trap mode and look at high end speaker makers.