Any question answered...

Most PA systems use high impedance (100Ω) speakers, so high voltage and low current in the speaker cables. Domestic HiFi uses 8Ω impedance speakers, which need lower voltage and higher current to transmit the same power from amp to speaker. This makes it safe to have bare terminals where the kids and pets can get hold of them, but does need fatter wires.

PA systems (that aren't megaphone/tannoy style) are all 8ohms, or possibly 4ohms if mono and bridged. The sound quality and relatively small distances involved in cinemas, would suggest they're using normal low-impedance systems and not 100v line stuff.