I have a line 6 spider valve 212 mk1 40w combo amp. Im looking to attatch an extention 4x12 cabinet to it for my bands live performances. I have 2 celestian 16 ohm speakers. What speaker specs for the cabinet as far as ohms can i use to work with the combo amp... i have multiple output jacks..... 8 ohm pair, 4 ohm single, 8 ohm out, preamp out and power amp in. along with a direct out. Which of these can u use with a compatible cabinet, and what would the specs of a compatible cabinet be?