Just to add with my "using internal speakers and a single QSC cp8"...
one of the downsides of using a single speaker (not a sub) is that as you turn that speaker up, because you're summing the output to mono, you loose some of the niceties of the effects.
In particular the rotary effect doubles in speed (normally it would flip from one speaker to another but because you have only one, it sounds like the rotary is almost a tremelo). This only happens when you turn the single speaker up to a point where it is louder than the internal speakers.....
Worth noting that if you give a mono feed to a PA this will happen too.....
The answer is as above, use a sub if that gives you enough welly coupled with the internal speakers, or use two external speakers (and a sub if necessary)......
If I do any louder gigs regularly, I'll buy another cp8 as they are a lovely, portable speaker, and they're flippin loud!