I'm having some problems figuring this out. I just joined a 12-piece band (2 guitars, keys, drummer, 2 trumpets, t-bone, 4 vocalists and me) and I'm afriad that my Mark VI isn't cutting it. It overdrives easily at the volume of the band. The head is rated at 400W in 2 ohms and 250 in 4 ohms. I play through a 15" Black Widow rated at 350W continuous at 4 ohms. I have pre and post at 6.5 and 4 respectively and something is overdriving. At those settings and the listed gear, what is maxing out here? Second issue. I'm thinking of adding this. 400W at 4 ohms(won't buy until I learn some more) http://tinyurl.com/fmqje If I add this to my existing setup, total load will be 2 ohms, correct? Would this then open up the 400W into 2 ohms that is rated on the head? When do I have to take into account the individual speaker ratings of the 1820? I hope this doesn't sound silly. I'm trying to learn a little more. Thanks in advance.