Speaker sensitivity probably has the most to do with volume potential of a system. Home hi-fi speakers might be as low as 85dB/W@1m, whereas serious pro speakers are better than 115dB these days. The home speakers would need 1000W to put out the volume the pro speakers could with 1W! But the Loudness War is really about prerecorded music...
The best practical place to control system volume is at the input of the amp. Slightly less-optimal choice is at the preamp's output to the amp. There are lots of articles on how to set up the gain stages in systems:
What Is Gain Structure at diyaudio.com
Setting Sound System Level Controls at rane.com
BTW, compressors and limiters can be fancy and fascinating, but there are "automatic volume controls" as well:
AVC-2 from Formula Sound
Useful for pro applications where you want to automatically cap the volume of the music, but allow speech (PA) between songs to be loud and intelligible.