Ok, I have tried to hook up two of my computers to my Harman Kardon AVR 154 receiver, and cannot get either one to produce any sound through the HD audio output.

One is a home-built desktop with an EVGA 650I Ultra motherboard.
The other is an ACER Aspire 5739G laptop.

Both are using Realtek HD audio, and have a headphone-jack SPDIF output. I connect them to the AVR (optical cable with the mini-plug adapter), select the optical input, but no sound comes out. The cable and channel on that receiver are good - I use it for a PS2.

For both systems, when I plug in the cable, it lights up the analog "audio out" connection, and does not register as the digital connection.

I'm doing something wrong here, can anyone help me?

Are you sure both PC's use "optical" audio outputs? Perhaps it's a 3.5 mm stereo/coax output.

The connection is through the same jack as the analog headphone jack - it's labeled for both. I have the mini adapter for the optical cable. Should I use a coaxial cable instead?

Well.. let me ask this rhetorically. Do you know of headphones that connect directly to an optical jack? ;)

S/PDIF does not mean optical only.

Question:
What does the plug that goes into the computer(s) look like?
Something like this?
http://www.amazon.com/RCA-Stereo-Cable-3-5-Plug/dp/B00021ENXM


EDIT:
This may be what you need:
http://www.ramelectronics.net/audio-video/custom-audio-and-video-cables/rca-to-3-5mm-s-pdif-cables/custom-series-spdif-cable-digital-audio-3-5mm-to-rca-spidf/prodSPDIF.html

Did you select "S/PDIF" or "optical" output in the Realtek control panel?

Ratman, I have the adapter from a Turtle Beach Audio Advantage Micro:
http://www.turtlebeach.com/products/micro/home.aspx

The Micro has a mini optical output, but will take 3.5mm stereo RCA in the same jack. I'll order that other cable and see what happens.

amicusterrae, I can't select the output - there are 4 icons: Mic, Line In, Headphone, and Digital / SPDIF. The icons are not selectable, but light up whenever somethings plugged in. There is a spot to select the speaker config, but neither setting there produces sound through the connection.

When you unplug the optical cable from the AVR can you see a red glow in the end of the cable? If not there may not be signal on the optic line despite your efforts thusfar.

Well... that's a missing piece of info. ;)

Have you contacted TurtleBeach for assistance. I'm sure your are overlooking a setup/configuration setting when using the optical output.

http://turtlebeach.com/support/index.php?View=entry&EntryID=830516275

I am not actually using the Turtle Beach unit for this setup, just the adapter to connect the optical cable.

However, since there is no red glow I take it to mean that the other cable is the one I need?

lack of glow could mean a couple things. 1. The hardware isn't working as expected. 2. the computer software setup isn't configured correctly.

It could even be both at the same time. You might try verifying with the other cable type if it is easy to try and eliminate 2 as being a possibility.

Unless the sound cards specify use of the Turtle Beach adapter, that adapter isn't likely to help you. It seems to be a way to use the headphone jack "hole" in the turtle beach device to "reach" a separate optical output built into the turtle beach USB device. You may rest assured that the adapter is just getting the optical output already present somewhere inside the turtle beach USB device to "talk" to an optical cable. It does not contain the necessary capability to convert coax digital to an optical signal, nor does it contain an analog to digital converter to take the analog signal and make it an optical digital signal.

You need to figure out what your actual sound cards output and connect the appropriate kind of cable to utilize that output.

You can use all of the 3.5mm optical adapters that you want, but if your audio outputs (jacks) on the PC's are the not optical, it ain't gonna work! (even if they "fit")

It is an adapter... not a converter. ;)

Plug headphones into the output. I bet they work. If so, refer to post #4.

Ok, so I just got in the cable from above, and I'm not having any more luck than before. The laptop recognizes that a cable is plugged in, but it registers as stereo output, not digital...

When you right click on the little speaker Icon in the tray and select playback devices is digital output selected as the default and windows says it's working?

Open "volume control"
propeties
check "DIGITAL OUT"
uncheck "Mute"

Just a guess...


Wow... you are not alone. :)
Now I'm not sure if your S/PDIF is optical or coaxial, but a least you have both cables anyway! ;)
Found some reading for you. Good Luck!
http://www.tomshardware.com/forum/243197-28-realtek-audio-surround-sound
http://www.tomshardware.com/forum/254601-28-realtek-digital-audio-problem
http://forum.notebookreview.com/showthread.php?t=308543