I suppose hooking up a multimeter to the speaker jacks on the back of your receiver, and monitoring the volts, then converting that to watts would work, if you want to take all that time.
Or you could probably estimate by using a Radio Shack SPL meter from 1meter away from a speaker. The problem is that music fluctuates and is so dynamic, it would not be 100% accurate.
The m22's give you 93dB (very loud) only using 1 watt at 1 meter. So monitoring dB from 1 meter away, you could estimate how many watts your using.
1 watt = 93dB
2 watts = 96dB
4 watts = 99dB
8 watts = 102dB
16 watts = 105dB
32 watts = 108dB
64 watts = 111dB
128 watts = 114dB
you get the picture, do you see why your receiver is adequate and you most likely don't need an amp.