jiobao,
I don't think you'll be satisfied with only new speakers. It sounds like you want "cleaner" sound. The only way you will accomplish this is with mid- to high-end "clean" power. Just because a mid- to high-end system will make your ears bleed, that doesn't mean it is all it's good for.
The last system I built (about 12 years ago) was only rated at about 310 watts RMS, but, it was a high quality Kenwood system. It started with the competition deck, which had no amplifiers built-in, which pushed a very clean pre-amp signal. I paid about $700 for the deck and it was the anchor of the system and well worth the cost. A comparable one today would run about $450 (I would recommend Eclipse). After the deck, the next most important, yet usually overlooked, item is your wiring. You need top-notch RCA cables to get that "clean" signal to your amps, heavy enough power and ground cable to feed the amps the power they need, and heavy speaker wire to get the "clean" sound to your speakers. You don't need extremely powerful amps to get great sound, but, you do need to make sure they are high quality. I had a kenwood 40w RMS x 4 channel amp pushing four kenwood 6 1/2" 3-way speakers and a kenwood 150w RMS sub amp pushing two tens in a bandpass box. This was a total of 310w RMS but believe me, it would make your ears bleed. The thing was, the sound was extremely clean all the way through the volume range.
I probably spent a total of about $1500 (I installed it myself) on the system and it could probably be duplicated today for around $1200 or so. If you just replace your speakers, you probably aren't going to get what your looking for.
The shaker is a decent production head unit, but, it is far from a high-fidelity type unit that is going to put out the "clean" sound you are looking for. You could put in the best speakers money could buy but they will not overcome a sub-par head unit putting out a signal that is not up to your standards.