Hello
I am by no means an audio expert, but I have done some hookupsand configs of PC's with speakers, etc.
I also have an Audigy 2 ZS card and I am getting the Z5500's soon.
This is what I found from support at the Logitech site at logitech.com.
Let me know if this helps!
I think what you need to do if you are using an coax connection from the Logitech controller to your soundcard: you need to disable the digital decoding that goes through the soundcard and enable the controller to handle the digital decoding on its own.
Here's the step by step instructions:
How can I get Digital 5.1 Surround Sound on my Z680/Z5500 via a Sound Blaster Audigy 2?
Answer
The Z680/Z5500 come equipped with both digital coaxial and optical inputs. The unit also contains a digital decoder that can decode either Dolby Digital or DTS signals, which you may connect to your computer by a 75ohm digital coaxial cable or standard optical cable. The onboard decoder must be used in order to experience true 5.1 surround sound. To use the Z680/5500 onboard decoder, the speakers must be connected to your sound source or PC via digital optical or coaxial cable and the "effect" setting must be set to PL2 Movie for DTS and Dolby Digital on the Control Pod. In general, you must disable any software and/or hardware decoder on your PC. You will need to do this because the Z680/Z5500 decoder will not be able to decode an already decoded signal. If a software or hardware decoder on your PC is active, the Z680/Z5500 will play the audio in only 2 channels, rather then 5.1. You must also remember that the source of the audio must also support 5.1 Dolby Surround or DTS, such as DVD movies and some video games.
Step 1: Before configuring your Sound Card
As stated above, you'll need to disable your onboard hardware decoder. To do so, you'll first need to go to the Creative Labs website and download the latest software and firmware update for your Audigy 2 sound card.
Step 2: Configuring your Sound Card
Once you've downloaded and installed the latest updates for Creative Labs, click the Start button, go to Programs, select Creative, then to Sound Blaster Audigy 2 menu, and finally select Creative Audio HG. A window will pop up; double-click on the "device controls" icon. Another window will appear in which you'll need to select the Decoder tab. In there, you will see two options. Select the second option, which states "SPDIF Passthrough (dolby digital/DTS out)". This will turn off your onboard decoder and let the Z680/Z5500 do the work. Then click close.
Step 3: Configuring your Speaker Settings
Now, you'll need to go into the speaker settings control panel. To do this, you'll need to go to the Start menu, Programs, Creative, Sound Blaster Audigy 2, and then click on Creative Sound Mixer. In this new window, you'll see three icons at the bottom. Click on the second speaker icon. Now from the drop down menu, select 5.1 as your speaker selection. Then check "synchronize with control panel". Also, make sure "digital output only" is selected. Close the speaker settings window and restart your machine.
Step 4: Testing your Sound Card
Once your computer has restarted, go back into the speaker settings. This time, click on the "channel" button. This will test all your speakers one by one. You should hear "front left"... "center" ..."front right" and so on, coming from each speaker.
Notes:
Now you should be setup for digital surround sound although there are a few things that you'll need to take note of to get DVD's and games to work properly on your computer. Inside your computer, there must be a digital audio cable connected to your DVD-ROM to your sound card. Also, the DVD-software may have an option for software decoding and this option must be disabled. Finally, the DVD movie or game you are using must support 5.1 Dolby Digital or DTS. Sometimes you must go into the audio menu of the movie or game and set it to 5.1 DTS or Dolby digital. If you are still experiencing problems with digital 5.1 surround sound, you'll need to contact Creative Labs or the software player manufacturer you are using.
