can you be more specific?
Perhaps you can say what you expect to gain by upgrading. If there are things you don't like, what are they? Lack of resolution, coloration, fuzziness at loud levels? Certainly you can describe something about your expectations for upgrading. Throwing out a couple of model names is not adequate to help someone give you a useful recommendation. From what you say, your cheap subwoofer could be screwing up your whole system. If you've got overlap, it will muddy up everything. You need to make sure your mains and the sub are not duplicating any frequencies, and that the problem is not room resonance. For $5, download an audio test program for your computer and get a Radio Shack sound pressure level meter and do some slow frequency sweeps and find out if you've got a problem.
If your objective is to make the music more defined and detailed, and your imaging is ok, you're probably only going to do this with speakers with large cabinets that reduce the driver backwave energy that is not absorbed, and units with additional drivers mounted in a vertical row to increase power handling and headroom so that audio peaks are still smooth and relaxed. Upgrading to a model that still has only one tweeter won't do that.
If your objection is coloration, which is almost unavoidable in all modest size enclosures, consider a pair of the smallest 2-way Magnepan quasi electrostatics, about $750. They'll still need a subwoofer and have to be set up carefully, but will produce an openness and coloration free sound not available from any box. However, they're not real good at LOUD.
Your original question presumed that the improvement you sought was a matter of speaker and amplifier brand matching. As long as they don't run out of power, the differences in amps are way small compared to the differences in speakers. I would bet that if you can articulate what it is you hope to acheive, the solution will have little to do with your amp.