Hearing response is logarithmic, meaning that you need 10 times the power to double the volume.
Because the mixer has 6 inputs does not mean that you can have electric guitars, electric bass etc plus vocal mikes. The bass in particular will sap the power of the amp and knacker the vocals. Next thing that will happen is that the amp is overdriven causing clipping. This means the output goes DC and burns out the tweeters. The sound is now pretty crappy so a well meaning helper will crank up the EQ to get more top end. Pretty soon you will burn out the mid range drivers as well, and maybe the output stage of the PA for a bonus.
(a 20 Watt amp can burn out a 500 Watt speaker if it is overdriven)
When the repair bill comes in it will all be your fault because you bought the wrong gear in the first place.
Enjoy!

I can't get this post to stick, one more go then I give up perhaps it is too early in the morning