Originally Posted by MalcolmW
Check that you have the outputs on the HD621 connected to the correct inputs on the G68. It's very easy to get this wrong.

Problem solved. I am blind. I couldn't read the legends on the back of the G68. I had the cables connected from the HD621 to MD1 on the G68 in reverse order. Who would have thought the order of the jacks would be L/R, C/Sub, Surrounds from RIGHT to LEFT instead of left to right?

I still don't understand why I didn't get anything out of the center channel as it was correctly hooked up even when the order was reversed. That will have to remain a mystery.

561, DSP5500s, DSP5000C, analog sides and rears