The safest and easiest solution may be a separate speaker switcher, which allows you to connect as many as four, six or eight pairs of speakers to a receiver or amplifier.
A speaker switcher is necessary to protect a receiver or amplifier from low impedance problems caused by playing multiple speakers at the same time. Here's why: A receiver or amp is usually rated for speakers that have 8 ohms of impedance. Some are rated from 4-8 ohms, but 8 ohms is the norm. The impedance specification is important because it determines how much electrical current flows to the speakers and connecting multiple speakers increases the flow of current from the receiver to the speakers. For example, if two pair of 8 ohm speakers are connected and playing, the resulting impedance is 4 ohms. Three pair results in two ohms, and so on. If the current flow increases too much, it exceeds the ability of the receiver and the result is the receiver activates its protection circuit and temporarily shuts off. Most receivers can handle four ohms, but two ohms is the limit and will likely trigger the protection circuits.
The solution is a speaker switcher with impedance matching. With a switcher you can safely play as many as four, six or eight pairs of speakers simultaneously and the impedance stays at 8 ohms, thus protecting the receiver. To use a speaker switcher, connect the left and right channel outputs of the receiver or amp to the inputs of the switcher, then connect the various speakers to the speaker outputs on the switcher. Here is how to run speaker wires to other rooms in your home.
There are a wide selection of speaker switchers available. Here are a few links to compare features and prices: