Home-made gaming PC (pretty modest, don't get any ideas), running Win XP (yeah, I know, but it's fine by me), using old-ish AMD dual core on an AM2 socket. It's connected via HDMI (through a DVI/HDMI converter) to a plasma TV, and via S/PDIF to a home theater amplifier. The TV is itself connected for sound to the home theater via an optical cable, which is rarely used (more about that below).
I took out the old 9600 graphics card and replaced it with a new GTX 560. The installation required the manufacturer-provided CD to install some drivers. Fine, I did that. Then I downloaded and installed the latest GeForce driver from NVidia.
This computer has and old Audigy sound card, without the breakout box. I use it because it works, and because I managed to get true 5.1 audio from its digital output to my home theater over the S/PDIF cable. 5.1 normally works only over the analog outputs; however, I installed some software (can't remember the name right now) that encodes the sound on the CPU in real time and sends it out over S/PDIF as 5.1. Everything worked perfect.
Now here's the thing: after finishing all chores related to the GTX 560, the Audigy card disappeared from the settings. I cannot select it as an audio output at the OS level, and sure enough there's no sound coming out of it.
However, the GTX 560 now acts as a sound device. It's sending out sound to the TV via DVI/HDMI. I could route the sound through the TV to the amplifier, no problem. But the thing is, it doesn't seem like the 5.1 surround works correctly. I tested some games (Portal, Civ V, Moonbase, Spore) and the front / rear separation doesn't seem to work; it's as if the rear speakers are only used for echo and ambience. It's like the Audigy over S/PDIF before I installed the real-time sound encoding software.
In Control Panel, I configured the speakers as 5.1, but it didn't help.
What could cause the disappearance of the Audigy card? Could the Gigabyte installer be so nasty as to remove the drivers for the Audigy?
I could live with the GTX 560 as a sound card, in fact I would prefer it, provided that I re-enable true 5.1 with front / rear separation for the games. Any suggestions?