Here's a way I thought of to measure the RMS output power of an amplifier. You need to know the speaker impedance, which is not quite the same as the resistance you'll measure with an ohmmeter. I've heard that Bose systems use 1 or 2 ohm impedance speakers.
If you don't know the impedance you can break the circuit to the speakers and insert an AC ammeter in series with the speaker to get a current reading. Otherwise, if you know the impedance you can calculate the current from the voltage.
Get a test CD with a sinewave test tone at a consistent level. Also get an AC voltmeter (a multimeter set to the AC range will work fine).
With the AC voltmeter hooked across the speaker terminals and the test tone playing, turn the volume up to just below the point at which you hear distortion. Note the AC voltage reading at this point. Also note the AC current if you are measuring it directly. (Ideally it would be best to use a scope to verify at which point distortion occurs, but not everyone has one of those...).
Now you have the voltage and the resistance (impedance). From there you can figure current by using this formula:
current = voltage / resistance
Or you can use an AC ammeter to measure the current.
And once you know the current you can figure out the wattage:
watts = voltage * current
And that should be the RMS output wattage.
(Note that all AC meters are calibrated to give the correct RMS current and voltage when dealing with a sinewave. It's when the wave is not a sinewave that they don't give accurate readings and you need a tru-RMS meter).
