Hello,
I do not mean to hijack your discussion but, I think I might be able to help. I looked at your block diagram and saw something that might be causing some confusion. On the input side, you have an HD-SDI (digital) signal being converted to analog and mux'ed with a composite (analog) signal. The output of this mux (analog) along with an audio signal that has been digitized are prepared to be transported.
After the signal is transported, the output looks to be RGB (digital) data and an analog audio stream. I assume digitized video data because of the "RGB" in the SDI block and the encoder leading into the composite output.
Maybe clarifying the state of the audio and video to be transported would help Dave and the product lines come up with a possible solution.
This is just something I noticed and thought might help. I will get out of your discussion now!
CE
P.S. You mentioned the customer only mentioned standard def but I believe the HD-SDI (292M) is defined for 720p and 1080i.