Fog, definitely get the CD player off the top of the receiver so that it has a better chance to cool. While running two or more speakers in parallel serves to reduce the net impedance(the sum of the reciprocals of the individual speakers equals the reciprocal of the total impedance, e.g. 1/8+1/8+1/8=3/8 or 2.66 ohms), you say that it shuts off now when even one set of speakers is connected through the switching device. Despite the experience of the installer, I'd question whether the connections are correct.
