Hi Guys    i need your wisdom please    I have just bought the Orange terror amp 500 and the OBC115 cab   I am quite new to this so please go steady :0)   the terror amp is 500 watt and the obc115 is 400watts , on the back of the amp is a switch for 4 ohms and 8 ohms i have no idea which one i should be choosing ( i dont want to damage anything)   its quite confusing what option i should use- your help is appreciated