Amplifiers are rated in wattage output at different impedance levels, called ohms. Impedance is voltage resistance, is dictated by the connected speaker, and allows power to come from the amplifier. As ohm loads decrease, the amplifier produces more power. Connecting speakers with ohm loads that are too low will cause the amplifier to blow. Check both the amplifier's ohm and wattage ratings, which are usually printed on the back of the units near the connection points. Always make sure that the speakers are compatible with the amplifier in wattage and ohms before hooking them up.
When multiple speakers are hooked up to a single amplifier channel, the overall ohms will change according to the way the speakers are connected. When wiring speakers in series (each speaker cabinet connected to each other), the ohm load increases, causing amp wattage to go down. Wiring speakers in parallel (each cabinet connected directly to the amplifier), causes ohms to decrease and amp wattage to go up. Consult the amplifier's owner's manual or web site for particular information on recommended wiring of multiple speakers. Guessing or experimenting may result in serious damage to the amplifier, and possibly the speakers.
Choosing the right speaker wire doesn't have to be expensive or complicated, as all the speaker wire needs to do is carry the proper amplifier voltage to the speakers. As a general rule of thumb, long speaker wire runs and low ohm loads require thicker wire. If the wire is not thick enough, volume loss can occur, and you won't be running your gear at the most efficient level. Make sure your speaker wire is adequate, by consulting one of several excellent web resources for determining speaker wire gauge. If your wire is 14 to 10 gauge, it is sufficient for all but the most extreme speaker and amplifier wire lengths and ohm loads.
Power amplifiers feature one or more speaker connection types. Among the most common are: wire post, 1/4 inch jack, and Speakon. Advantages of one over the other are debatable, but whatever connection you choose, ensure that the speaker wire size is not compromised. Standard 1/4 inch plugs are too small for heavy gauge wire, but you can purchase jumbo plugs to accommodate. Wire posts are at a disadvantage when using heavy gauge wire too, by the wire ends can be fitted with soldered terminals or "banana" type plugs to overcome this. Don't cut wires strands to make the connection fit, but use the proper connector for convenient, safe and efficient results.