I mean, the easiest way to get a line-out is to just hook it up the speaker out pads, something like:
[SP+]–[100ohm]–[1uF]–[LineOut+]–[10Ohm]–[LineOut-]–[1uF]–[100ohm]–[SP-]
The SP+/SP- is 10v peak-to-peak, and if my math is right, something like this would bring it down to ~0.5 volts.
SPDIF should also work though. I’m not sure why it wouldn’t.
Have you tried using a digital analyzer to see what signals you’re getting out?
Absolutely, inquire away. 
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