Peak Music Power is measured in Whats, not in Watts.
Little computer speakers are powered with a 12V/1A power supply (12W) and are rated for 1000 Whats.
i like that..... that explains the sony low-fi monster boom box systems with a 100 watt transformer that has "300W" plastered all over the box, and the advertizing blurb says "6000WATTS PMPO!!!!!!" it has two 50W amp chips in it for the woofers and a dual 30W amp chip for the tweeters..... (picture shown below)
they should change the term to"Whats" when they stretch the truth so far beyond the physics that it's unrecognizeable as reality. i guess the 6000W PMPO is measured in the microsecond before the amp chips let the smoke out during testing.......
i think the OP's confusion is the LM386 having a gain between 20 and 200, and mistaking this for DB's. the gain is simply 20 to 200. dbs are sometimes used by some manufacturers for measuring op amp gain, when the gain of an op amp is in excess of 100,000. saying the gain is 50db takes up less space in print.
db measurements have a certain amount of confusion associated with them for most people, because there are so many different ways they are used. you have db, which is just a ratio, such as between input and output, you have dbV which is compared against 1 volt (including dbmV or dbu for 1 mV or 1 uV) for signal levels, or dbmW (sometimes written as dbm and dbW would db compared to 1 watt) for comparison against 1 milliwatt. you will sometimes see dbc, where harmonic content or noise is compared directly to a carrier level.
with audio you will see distortion measured in db, such as -70db. technically, this should be written as dbc, because it's compared against a signal level.
or you may see the sensitivity of a speaker written as db@1m, for instance 90db@1m which is the sound pressure level (SPL) measured 1 meter away from the speaker at 1W input. from this (and here is where Watts comes into the equation) you can calculate the SPL at any wattage within the capabilities of the speaker. so at 10W (10dbW), you get an SPL of 100db, and at 100W (20dbW) you get 110db SPL.
these are some of the ways that db measurements are used, and also why there is so much confusion about their use.