Erm, I have a cable that you can plug at the same time. It comes with the Xbox 360 Elite and it has both S/P-DIF and analog L/R.
Edit: this one: http://i16.tinypic.com/4r7rej7.jpg
Yes I have that also but it outputs nothing to blackmagic… Strange… Must be a setting o something
The AV component connector that comes with the 360 won’t let you use HDMI simulaneously.
Click on this link. Some people have been having issues with no sound coming out of the hdmi cable because of the NXE update.
Oh yes, I forgot NXE fucked up HDMI, that might be the cause.