When going with a passive PA system, choosing the proper amplifier and speakers is extremely important.  

An often misunderstood specification. Measured in watts, it is best represented by RMS (root means square.) This figure tells us how much power the speaker can comfortably handle for a sustained period of time. Also referred to as continuous, or nominal power.

- Focus on RMS power ratings.  

- Determine what the RMS power rating on your power amplifier is... Let's use the XGA-5000 as an example (2 x 400W RMS) @ 8Ohms.  What does this mean?  The XGA-5000 is pushing it's max clean single 400W to each unit per channel to an 8Ohm speaker.  You would then need to find an 8Ohm speaker capable of handling 400W RMS max.