What to know about Bose

Originally Posted by Fountainhead

OK,
Bose spkrs are typically very low ohmage to maximize the power from the 12V rail. If you connect higher ohmage speakers then the available voltage is divided across a higher impedance/resistance, causing less power to be available from the amplifier. P = V2/R, so if the voltage stays the same (relatively speaking) then the R produces a lower power number.
Running higher impedance speakers only lessens the power output, running speakers with lower rated impedance can cause the R number to get too low and cause the power to exceed the heatsink capability of the amplifier, causing repeated thermal events and eventually damaging the amplifier.

The end goal is to select speakers that match the ideal load for the amplifier, that produce the desired frequency response, and hopefully you've selected speakers with high efficiency, i.e., if you have speakers that are 90 dB efficiency, then if you substitute 93 dB speakers, it's like getting twice the sound pressure level with the same speaker.
Also, if you have one 90 dB efficiency speaker and add another 90 dB speaker, then your SPL level will increase 3 dB.