Yes, it would be possible to run the sub out signal through the line in connectors. Just find which wires they are on the dock harness inside the Empeg.

Yes, it is true that the sub-out board is an add-on to the digital out board. Here's why: The signals the sub out board uses are too weak to run unbuffered. The digital out board has a buffer that buffers all I2S and clock signals. There is a spare line in the buffer for the sub/ center out channel (the Serial Data 2 line from the Empeg). By using the existing buffer on the digital out board, it will make having both the digital out board and sub out board inside the same player a much more feasible proposition, as the sub out board can be that much smaller.

Stu