A speaker's power handling is a really complex metric. Whenever a manufacturer gives a single number (and practically all of them do), it's to be taken with a huge grain of salt. The power that can be handled depends on the frequency of the signal, its amplitude, and its duration. A single number can't encompass all the variables.
For example, they can probably handle 300W in bursts of a few milliseconds, but a continuous 300W signal will fry them. And they can probably handle 300W at certain midrange frequencies, but a 300W output in the low bass will send the woofers crashing to their ends.
As I said before, a higher power amp might get you a little more output, but remember that doubling the power only nets 3dB, a relatively small increase in perceived loudness. So a 300W amp will allow you to play a little louder but now with the higher risk of damaging the speakers.
So, really, either stick with what you have and save your money (and your hearing), or if you want louder, get more efficient speakers.