It's a powered mixer, so I'd always run it with passive cabs connected. If you needed extra noise, you could always add active( powered) ones from the line /amp outputs. Never never never connect active cabs to the Speakon outs on the mixer.
I've just read the specs for it, and I'm not entirely sure of the power ratings, whether they're RMS or not. If they're anywhere near what they claim, you need some fairly serious speakers for it, something of the nature of the Pavey UL series, the Electrovoice ZX4, there are some Dynacord and HK cabs of a suitable rating also, but they're not cheap. I have no experience of the cabs I've mentioned, just that I believe they're the sort of power handling you need for the mixer.
I'm sure someone with experience of the beast will be along soon.