I'm with Data - the speakers are the link in the chain closest to you (apart from the room) and you need to find the right ones for you first. Then find an amp that drives them properly and gels with them. Then when you've saved up a bit play around with disc spinners until you find just the right one for your amp/speaker/room/music tastes combo. IMHO of course.
Now to your system. I would say the call to upgrade your amp is perhaps a bit premature. If I'm not mistaken the C350 isn't half bad and has a fair bit of grunt on offer. I would swap those Crestas for a nice new (or s/h

) pair of speakers before messing with anything else.
At the top of my list for your budget would be the ATC SCM-7s and secondhand Dyn Contour 1.3 Mk. IIs. Both of these speakers are truly excellent, though the ATCs might suit your room better, being smaller and sealed box to boot. Speak to Michaelab about the Dyns.
As for the ATCs I think you'll find they have the best midrange, and some fo the tightest, cleanest, most dynamic bass of any speaker near their price range. The integration of the drivers is also absolutely spot on and they time like nobody's business. They are also very high resolution yet natural and unfatiguing. I think you'll like the way they do female vocals. And they also won't be embarrassed by even very high quality amplification (for one thing, they're rated to 300 watts so they love power). Maybe you could go for one of the abovementioned Rotels? Naim are also said to go very well with ATC speakers.
I also wanted to mention something about the MA Silver speakers. I had a demo of the Silver S6s fairly recently, alongside some other similarly priced floorstanders. They sounded very good for the most part but they still haven't gotten the metal dome tweeters right. When I played [one of] the Spanish guitar track on the recent Hifi Choice Naim sampler CD, the MAs made the Spanish guitar sound like a very convincing steel string guitar. Really. Quite eye-opening.
Anyway, good luck. I'm sure you've got a lot to think about given the depth and breadth of the ideas posited thusfar on this thread.
Dunc