"I think of headroom as an amp that simply loafs along meaning the amp operating at their best sonic level and not strained often leading to increased distortion.
As always, match the amp to the speakers for best sonic performance results."
Say you choose a speaker rated at 86 dB at 1 watt, one meter (86 dB being quite loud already) and consider there will be a slight loss from the front of the speaker to your listening position and then room gain (boundary effects) will compensate for some of that loss. Also, the bulk of the program from any given source will only require microwatts to produce a comfortable listening level and 1 watt will be quite loud for most peaks, then any power required to hit levels above 86 dB will be headroom.

