Imagine you have to run an audio store.
>
> There are 20 receivers and only one 7.1 speaker set.
>
> You as salesman want to switch between the receivers as to compare
> receivers.
>
> How would you connect the speakerset to the 20 receivers and how would yo=
u
switch between them ?
7.1 speaker sets come pre-connectorized for the various amplifiers. No store wants to cut off the connectors (which would be required to wire in a switch assembly), so the store will have 20 receivers and
20 speaker sets (some of which will be 5.1, some 7.1, some stereo).
If the switching was really required (like, to allow a wall-of-sound set of builtin speakers for a home theater to be demo'ed), you'd probably wire speakers to a 24-pin connector (similar to the power plug on a PC motherboard) and for each amplifier have to custom-build a wiring harness to a suitable mating plug. Adding an A/B two-way switch would then require a switch box with two input sockets and an output plug. A full 20-way switch box is ... uneconomical.
While '7.1' only requires 16 pins on a connector, there will be unit- to-unit differences (powered subwoofer or unpowered subwoofer?) that will benefit from extra connection points.