Also, if you do that, put some wire between the resistor and the SSVC-6. We took one out of someone else's install where they had put a four ohm resistor in series with each channel, connecting the resistor directly to the SSVC-6. The resistor had gotten so hot during usage that it had mostly melted the plastic parts of the connector on the switcher.

Let's say there's no DC on the amp output: remember that a 250 watt amplifier that's not turned all the way up puts out much less than 250 watts. It might not be the amplifier power at all!

Download the instruction manual and follow the setup instructions. A particularly important step in setup is how you set the power amp volume. You will have problems if the power amp outputs more than it needs to output to satisfy the volume requirements of the system. In brief,
set the impedance control properly, per the manual;
turn the SSVC-6 controls up ALL THE WAY;
turn the power amp up enough to hear sound in all locations;
walk from room to room and find the one that is the lowest in volume;
and set the volume of the power amp for the loudest volume that you're going to want to have in that room (all other rooms will play louder so you'll have to lower their controls more than the control for this room).
If possible, at this point remove the client's ability to adjust the power amp's volume. If not, someone some day will decide that more volume is needed, and instead of turning up a room control, they'll turn up the power amp.

This guarantees that all rooms will play loud enough and the amp won't play too loud. If the thing knocks then, you simply can't use this approach.