How can i get more power through 8 ohm speakers?

In addition to the impedance rating of a speaker, there is also a wattage rating. Ideally, power output of the amplifier should not exceed the power handling rating of the speakers. The input impedance of the speakers should match the amplifier output impedance for maximum power transfer (Rin = Rout where R is resistance in Ohms). Supplying more power or wattage to the speaker than it can handle will result in distortion, and if the output of the amp is high enough and present long enough, it will damage the voice coil of the speaker. Make sure that when comparing wattage ratings, you are comparing the same rating between amps & speakers. Watts can be expressed three different ways: "Peak", "Peak to Peak" and the industry standard "RMS". The relationship is such: an industry standard value of "70 Watts RMS" (70W RMS) equals "100 Watts Peak" (100W P) *and* also is the same as "200 Watts Peak to Peak" (200W P-P). Furthermore, there is no such thing as 200W "Music Power" (but is often expressed this way to inflate the RMS wattage rating (and usually is close to the P-P rating). A speaker is an electrical device, so most the things that happen to electrical devices when over powered can happen to speakers and amplifiers, too.

Increasing the signal source level (input signal to the amp via volume control) in an attempt to get more audio power to the speaker can overdrive the amplifier - resulting in "clipping". This is plainly heard as "muddied" sound. The otherwise loud, crisp, clean passages in music end up sounding garbled and unpleasant when an amplifier is over driven in this way. This can damage both the amp and the speaker.

Cheap amps with higher THD (total harmonic distortion) ratings sound worse than their counterparts with a lower THD rating - when all other variables are the same. You'll pay extra for lower THD values.

You might be able to make a speaker seem louder by positioning the speakers against a wall, on the floor, etc. Experiment; as it can make a significant difference in sound levels and low frequency bass sounds.

I hope this was helpful!