I was gonna ask the same question as Dincz, but thats opened another can of worms for me! I understand the Ohmage side of things... Im looking at buying a new rig... but want to get the most efficient poissible. After reading this topic i've discovered that your cab should be around about half more than ur amp... so for example, if I had a 500W head, i'd need a 750W cab OR 2 x 375W cabs. And if this is the case, then you wouldn't be able to add or take away any cabs and would have to use the rig as it is... Is this correct??... Actually, sod it, i'm gettin a combo!!! lol