That depends on impedance of the speakers, and the "rated" impedance of the amplifier. For example...you could run 4Ohm speakers on an amp rated for 8Ohms. But most likely, the speaker or amp or both would be destroyed if you crank it up.
All amplifiers need a "load" on them. Some are rated to run safely with no load. But most often, the amplifier needs something to push, or it destroys itself. The load is usually a driver (speaker). The load (driver/speaker) needs to offer enough resistance to the amplifier. This is called impedance. The amplifier is rated for a certain impedance of load attached. The driver/speaker is rated to provide a certain amount of impedance to an attached amplifier.
If you cut the impedance of the load in half, then the apparent power of the amplifier doubles, IF the amplifier can handle the lower impedance. Or in other words, if you have a 1000W AMP rated at 8Ohms, and you drive a 4Ohm speaker with it, then the maximum effective power will be closer to 2000W. However, the amplifier might destroy itself at the lower impedance level. Ooops.
What's more important than output power us total harmonic distortion. Any amplifier of 5W or more can drive sound at a high enough volume to make your ears bleed. But if that amp has 20% THD, for example...then you won't get good sound out of it. And adding more power would just add more noise, tragically.
Most people think more power is better in a sound system. Not really. For your typical 80W per channel home theater, for example...
If you use 10W per channel, then your neighbors are going to be complaining. The neighbors that live on the other side of the lake, I mean. Always look for lower total harmonic distortion. A 5W AMP with .01 THD is going to sound a thousand times better (at any volume level) than a 5,000W AMP with 1% THD. Sadly, there are audio amps out there that proudly proclaim 10% THD or higher. (frightening...)