The sound card is mounted in an Alpha 2 on the right side. You can tell as it has a USB cable and an audio cable plugged into it. Follow that USB cable to the MPU. Label it so you know what is what. On my cab they all look the same so I label them. Just disconnect it from the MPU not the card it self. Much easier that way.
You will get rid of the error but the sound will be lower than normal games. You really have to crank up the volume in the menu. So when your not running a game with this error, I suggest plugging it back in.
If you still have trouble finding the sound card, let me know. I can take a picture when I am at my cabinet.