You should use CL2 for in-wall use. Although ratings are not covered, Aperion has a good article on choosing the gauge: http://www.aperionaudio.com/AperionU/choose_speaker-wiring.aspx
Someone will reply to this post saying you don't need CL2 because the wire doesn't get hot. But, your local building code probably calls for CL2, why be out of compliance if it's only going to cost a few dollars more?
Joe
If you can't have fun doing it, it's probably not worth doing.