Speaker-level impedance-matching selectors with attenuation - effects

[Clmrt]

My buddy has one amp/pre combo driving a piece of gear like this, in turn driving a kitchen set of B&Ws and a living room set of NHT floor standers.

I've always wondered how these impact a system's performance. Any insight?

I'm pushing him to utilize the preamp's tape-out to drive a little class D with attenuator like a Fosi.

https://www.crutchfield.com/p_190SSVC4/Niles-SSVC-4.html