Found the problem. It was apparently a short to the drive sled. I had insulated the sled from the board with some heat shrink tubing, but apparently it wasn't enough. After ripping the board from the sled and putting it beside the Rio, I immediately got perfect output.

For those wondering about volume control and EQ, they are both fully functional through the dig. output. One minor drawback is that there is no beeping with button presses. I will get to work on a SMT version soon.

Thanks for everyone's help making this project a reality.

Stu