Speaker Switch

I have a question about designing an audio system on my sailboat. I have a JVC automotive amplifier that supports two sets of speakers (front and rear), and as well has an audio line out.

My plan is to run three sets of speakers. One pair inside the cabin (8ohm indoor/outdoor speakers), one pair of outdoor marine speakers outside on the radar arch (for out on the open water....too loud for at anchor use), and a pair of Altec Lansing powered computer speakers in the cockpit (for use at anchor) wired to the audio line out.

I want to install a speaker switch so I can turn off the inside and arch speakers when I am anchored and just want to use the powered cockpit speakers (or a combination of the other two). The powered cockpit speakers have an on/off switch, so they should not be a problem.

So that brings me to my question. Speaker switches appear to be more than just mechanical switches. They purport to place a load on the amplifier when disconnected rather than just mechanically switching a connection to the speakers. So, my question is whether this is really necessary, and also, wheter doing this will increase the power draw on the amplifier.....as this is all being driven by battery power, I don't want to throw away juice unnecessarily when the speaker is "off".

Can I get by with a pure mechanical switch?

A modern solid state amplifier does not need a load. Simply turn off the speakers.
An old vacuum tubes amplifier must have a load at all times.
Vaccum tubes have not been used in car radios for about 57 years.