"Legambiente" wrote in message

I have a 20+ years old technics SU-Z400 amplifier still working well,
however I need to change the speakers because the rubber around them
is disintegrating and the the sound is distorted.

I noticed on the back of the amplifier a 2-positions switch for
impedance settings: one for main or remote 4-6 ohm (and main AND
remote 8 ohm) and the other for main or remote 8-16 ohm (and main AND
remote 16 ohm).

I suspect the switch has always been on the wrong setting (4-6 ohm) as
I have only a pair of speakers (main) with 8 ohm written on them. (The
impedance is always referred to each speaker, right??)

So if I buy another couple of 8 ohm speakers, should I set the
amplifier to the 8-16 ohm?

It probably doesn't matter that much one way or the other. These 8-16 ohm
switches generally changed the voltage applied to the output transistors.
The 4-6 ohm setting might put 35 volts on the output transistors, while the
8-16 ohm setting might apply 45 volts. If you don't really stress the
amplifier, the difference is mostly noticable on the test bench, not in
actual residential use by a conservative consumer.