Shmigsy,
Keep in mind, that adding an amp to an existing system is not going to change the sound one bit.
Nor is it going to make the system louder at a given level, provided we are talking about the level of the current unit in question at it's current calibration.
What it will do is give the ability to push it to a higher volume while remaining detailed without compression. In other words, it will take more to clip the amp.
IMO, the doubling of power argument is purely SPL. Has nothing to do with compression, clipping, are just the simple description of the sound falling flat because an amp ran out of gas.