Purchase a quality amplifier and replace the built-in speakers. It's not the cheapest, but the fastest option. The sound quality is much better if you connect a tube amp. Well, of course, the result will affect the volume of the reproduced sound. Mostly in showrooms and "prorolling" do with the power increase. Depending on the power amplifier will depend on the outcome. Wire from the amplifier should be short and thick to reduce the power loss and interference.
Replace the old speakers with the new. Select speakers with high parameter of rated capacity. This conversion will definitely affect the quality of sound output. But to extend the range of sound again, you will need an amplifier.
Increase the capacity of the columns using a special capacitor. He will monitor the cleanliness of channels and also affect the gain of the audio playback. This is mainly suitable for car audio system.
Install a powerful coil, if you have low frequency speakers. So while giving a powerful voltage it is not blown, install a system protection against exceeding the signal level and the heat sinks for the coils.
Contact a repair shop for audio equipment. Experts will do everything themselves and save you from unnecessary movements, freeing a lot of time. However, this will result in a certain amount, and services of "pumping" of the audio systems today are expensive.
However, if you still decided to engage in the improvement of its columns independently, remember that power is not the equivalent of the volume. And before to make some manipulations, calculate the permissible power for your apartment or where you will use the audio system.