Audio on v5.5 I/O Board

[bigvalen]

I don't seem to be able to get audio on any of the cores I've tried - using optical, or copper stereo audio wire with a pair of 3.5mm jacks.

Should the LED that's used for digital audio visibly flicker, or at least look dim, if it's flashing a few thousand times a second ?

Given I soldered it myself, it's very possible I screwed something up. Switches are set right. The LEDs light up on the I/O board. So...at least it has power