I was wondering what the rule is on bass amplifiers and cabs. My brother is looking to buy a new head and bottom and the store that he's dealing with has told him that you need to over power the cab in a bass rig. They're telling him that a 500 watt head at 4 ohms is a perfect match for a 400 watt cab at 4 ohms. They're saying that under powering a cab, such as a 400 watt head with a 500 watt bottom will blow the speakers faster than the other way around. They also said that you need to over power the cab in order to drive the low end and so that it's a clean low end. My brother looked at an owner's manual for a bass head and it cautioned that you should never do what the store is telling him he need's to do (at least with their product). He showed that to the salesman and he said he doesn't know why they put that in the manual because it's wrong! The store has my brother confused now because he's always thought that you need a bottom rated at equal or more watts. The salesman said that's true for PAs and guitar amps but not for bass amps. I told my brother that what the store is tellin him doesn't sound right to me. Am I wrong? Am I just adding to my brother's confusion? Thanks in advance for any advice on this situation.