I have been told that the way I set up my DRA-375RD could damage the receiver. I added a sub-woofer to the one of the speaker outlets. Today, the right side speakers no longer function (both sets of speakers). Could the addition of the sub-woofer have caused the problem? Or, what could be the cause?

Most subs are 4 ohm cabinets. That being said, if you added this to one of the channels alone, fine. If added while another speaker was also connected (A+B mode) and the other was a 4 ohm cab as well, then yes, you probably smoked that channel. The two 4-ohm cabs in parallel like that appear to the amp like a 2-ohm load. This amp is designed for a 4-ohm load minimum. It is likely that the output stage overheated and damaged the output transistors. I would have expected the amp to go into protect mode though. Let the receiver cool down and try again. If it works, then the problem is the low load and removing the sub will "fix" it. If not, then further examination of the output stage will be necessary.

Dan