It may help to further explain the reasoning in case popm8 doesn't know much about speakers. In VERY simple terms, the Ohms ratings are the impedence of the speakers which means how heavy the load the amp must "push" in order to make the speakers produce sound. Impednece affects everything from load on amp, to efficiency, etc, etc. Lots of reading is available on this topic. The most important thing to remember is this. Ohms ratings work similarly to guage ratings on wires (2 guage wire is bigger than 8 guage wire). The lower the number, the higher the load the amp sees. A 2 Ohm load is WAY harder to push than an 8 Ohm load. While most amps will be able to push a 6-8 Ohm load, be wary of pushing an amp with a 4 Ohm load unless it says it can do it. And by amp, I mean your AV Receiver since I figure that is what you must be using... Like I said, a very simple explanation... 8)
Thanks,
Wiley