Sitting down with a voltmeter and my spdif-coax equipped receiver, I
started looking for the proper pins on my "Thundering Digital 5.1"
6channel 8738 card.
It has a 2x5 pin header with one pin missing. Looking from under
the card (as in the writing is all in the proper direction) pin 1 as
per the below layout is missing. I've obtained a working spdif
output from pins 8 and 7, BUT, it is causing major ground loops /
interference in my home theater in the form as video noise. Has
anyone else got this cards' spdif out working? Do I need to use an
isolation transformer? I don't have access to a scope to properly
check the signal, but using my trusty voltmeter that output appears
to have quite a bit of dc offset. Do I need to add a decoupling
capacitor in line?

10 oo 9
8 oo 7 spdif out
6 oo 5
4 oo 3
2 o 1