Ok first of all, make sure it is plugged in the right place, which would normally be the pink connector.
After that, you probably have to enable it via software.
For instance, with my sound card, I had to open the eax console and check the karaoke box, then unmute the mic volume (because it's muted by default), then I can uncheck the karaoke box.
After that, on your headset you should be able to control the volume and the mic (on or off). Make sure it's on.
I have the audio .80 and I like them very much. The only drawback is that after a couple of hours, my ears hurt a little. I would guess that the audio .90 are more comfortable though.