It all has to do with impedance and sensitivity. Although Energy is nominally rated @ 8 ohm they also say minimum Impedance: 4 ohms. It could be they are drawing even more current from your reciever than the M80s will. The M80s are rated @ 4 ohm but pretty much stay around the 5 ohm mark. Combine that with the 93db rating the Energies have and it is not all that hard to see this happening.
When you say the drivers are really moving, be careful, if driven to hard with to much distortion it can very well cause driver failure.
