If I have 2x12" JL subs running 300 RMS watts each, powered by a JBL amp running 358 RMS watts to each sub, is that going to damage the subs? How much difference in wattage will be bad for subs? Im guessing 284 watts to each sub would not hurt them... Any suggestions/comments?
As long as your amp is supplying right around what the sub needs, you should be ok. Depending on what enclosure you are running depends on how much power handling the sub is going to have. Another thing you have to watch is to make sure that the amp you're running is going to put out the amount of power advertised. Some amps don't put that amount out, and some amps put more than that amount out. I think you should be fine if you're putting out almost 300 to those subs each. The JBL amps are decent.