Back to this one it's nicely made and cheap way of controlling up to 4 sets of Stereo Speakers on 1 Amplifier.
Though could easy connect 4 Amps to 1 set of Speakers, But be carful when doing either.

UPDATE after 3 years its gone intermitant [ Ссылка ]

A video on a 4 way switch box with protection can be found here,
[ Ссылка ]

An article here gives some information on protected switch boxes that multi speakers can be used without worrying about speaker impedance, [ Ссылка ]

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