Fred, "applied" wouldn't be quite the way to describe it. The arrangement can be looked upon as an internal "Y" from the pre-amp, with one branch for each channel sending voltage to the built-in output transistors for that channel and the other branch going to the pre-out. If the pre-out isn't connected to anything, no voltage is output there. No apparent reason for the Denon caution, since sending voltage to both the internal output transistors and out the pre-out to an external amplifier shouldn't cause any problem.
