The manual implys that you can just connect an emitter to the IR output and any IR signal that hits the receiver window on the 990 will be sent along out the IR output to the emitter. But I couldn't get that to work in various combinations of emitters / connection block.
The use of the 794-10 to interface with the 990 input seems well documented in the Saloon, but I haven't found any evidence of anyone being sucessful getting the IR output to work. I had given up...but since krisdz reopened this I do have one more thing to try this weekend.