i agree, the power is 18 "Whatts" at 10%THD, which sounds painful....... a more reasonable method of specifying output power is to rate it at some point on the curve where it is AT clipping (i.e. before the curve goes vertical). from the data sheet, i'd call it at 5 watts at 0.1%THD
the point of the mute pin is to have a time delay after power is applied before power is applied to the input stage, which avoids the huge THUMP. so the OP will need a circuit that waits a half second, before driving the mute pin high. maybe as simple as a transistor or two and an RC time constant