Connect 4 Speakers (varying OHMs) to One Amp

Hello Sonos Community,

I am doing a big bathroom renovation, and want to put 2 speakers in my "steam shower" and 2 speakers in the main part of the bathroom, for a total of 4 speakers.... all connected as one zone to one amp.

I have seen the documentation here that this is possible:
https://support.sonos.com/s/article/265?language=en_US#4_speakers

But, nothing is ever easy. :)

Since it's a steam shower, the speaker is going to get soaked. As such, I'm looking at marine-grade speakers.

After talking with Crutchfield, they recommended the "Kicker KM604W" speakers for inside the shower and the Polk Audio RC60i (or 80i) for the main part of the bathroom.

The issue, however, is that the Kicker marine speakers are:
4 ohm

The Polk speakers are:
8 ohm

On the Sonos link above it says:
To attach 4 speakers to a single Amp or Connect:Amp, the speaker impedance must be 8 ohms. Anything outside of that may damage the Amp, Connect:Amp, or speakers.

Yikes.... now I'm stuck!

I cannot seem to find any marine grade speakers that are 8 ohm.

I read online (after much research) that there are "Impedance matching speaker selector switch".
I cannot seem to make sense of that, so I don't know if it solves the problem or not.

Any insight is greatly appreciated in a big way.

Thanks!