How do I determine whether a switch can handle the power/current in a circuit?
Current and voltage ratings do not neccessarily apply at the same time and in a single operating point. A switch is a pretty good example for this:
it must not conduct a current higher than the rated current. This is relevant when the switch is closed.
a voltage higher than the rating must not occur between the switches contacts. This is relevant when the switch is open.
The current/voltage ratings may by no means be understood as a power rating and actually there is either voltage accross the switch (when it is open) or current through the switch (when it is closed). It's not possible to have both conditions at the same time and of course, the switch would never be able to survive a power dissipation of hundreds of watts.
That switch is for AC mains wiring at either 50 Hz or 60 Hz depending on which is prevailing in your locale. It is not rated for audio at all. So you just have to try it out and see if it works.
In general, lower frequencies are harder on a switch. DC is the hardest. Higher currents are hard on a switch. Higher voltages don't necessarily put a lot more stress on a switch. Some switches have the same current rating at 120 as they do at 240. AC switches shouldn't be used on DC at all unless you are willing to do your own validation testing or the voltage and current are negligible.
The problem with DC is that you get arcing that lasts for a relatively long time compared to AC. In AC, arcs get extinguished when the current passes through zero.
The switch might work for you if you stay somewhere around 5A. I don't see any harm in trying it. If the switch fails after a while you can put in a different one.
During switching there is more arcing at higher voltage than at lower voltage. Switches have a voltage limit, but they also have different current limits at different voltages. There are also wattage limits sometimes, and the rated limits may be different for different loads, depending on if they are resistive, inductive or capacitive.