How can I have different Audio output for Steam Voice chat?

Solution 1:

Using a program called IndieVolume you can choose which audio output a program will play off, unfortunately, splitting the two different sounds from within portal is not possible, so an external voice client must be used (such as steam chat).

Solution 2:

Unfortunately, something like this doesn't seem to be supported, yet. Most games allowing you to pick your output device for voice contents will allow you to select a second device/sound card to split output. You could try changing your default communication device under control panel's "Sounds", but I'm not sure if Steam will use/adhere to this choice.