Isn't there another complexity - continuous vs music power, as opposed to RMS vs peak? Music power is the transient power that can briefly be attained, which generally historically has been twice the continuous output, so peak music power = 4 x continuous RMS. As you say, PMPO is a random number - a quick check on That Ebay (looking for "pmpo computer speaker") shows some items with PMPO = RMS x 2, and one pair which has 80W PMPO = 6W RMS (incidentally, the ones with PMPO = 2 x RMS seem to have got there by thinking of a big number, saying that's PMPO, then dividing it by 2 to get RMS).