connect 3 pair of speakers to receiver
There are lots of ways to calculate the intended load, etc. However, the simplest thing to do is to buy a speaker splitter. Generally, they are specifically designed to combine multiple speakers in to the load expected by your amplifier.

And the device you linked to is exactly that: "... and maintains load at 8 Ohms".

Also, I have used that particular speaker selector. It's a pretty decent device.

One thing to watch out for is that some amplifiers don't like being suddenly disconnected from all speakers. Make sure that on the switch that you never turn off all of the outputs on a particular channel if your amp is on. The Yamaha amps I usually work with have no problem with this, but I have seen lower quality devices fry.