So i am reworking my stage rig a bit and need some help with what i plan to do.

I am building two new 3x12 (i know its an awkward/ less common configuration) cabs with 3 8ohm speakers in each. I don't have a problem with the actual construction i just get confused when matching impedance. I won't be using a head but rather my Peavey Classic 50 212 combo. It has an 8ohm extension cab input so how would i have to wire my cabs so that they'd work with the Classic 50 (running parallels or series etc.)

So basically i need help with proper wiring to match impedance and i guess how i should hook up the cabs. Could i run straight from the classic 50 into a 1/4" jack splitter to split off to both cabs or could i use my 12 input Yamaha mixer somehow in my set up to create more volume and crisper sound. Please help. Thanks guys