Here is a screenshot of my mixer panel:
Looking quickly at the STX manual you need to make sure that the mic source is deselected; press the button below the mic fader so that the red light is not lit.
Then activate the Line in channel by making sure the red button below the fader is lit.
Once that is done in Audacity you should be able to select the line in input mode; mine says "Line In (Asus Xonar D2 Audio Device).
I’ve tried it that way too, and I get a level of -16 instead of about -6. All sliders at max.
Reading the earlier posts in this thread more carefully I see you have been through some of this stuff already with Steve.
If your Asus driver is set up as mentioned above and you are still not getting any signal, go to the systray on the windows desktop and right click on the speaker icon and select ‘Open Volume Control’.
Then click options and select Properties and then click Recording and make sure Line in is checked.
Then examine the mixer window carefully and make sure that Line in is selected and if necessary uncheck ‘Mic’.
Hope that fixes it for you.
That is the correct configuration within the Asus driver.
I suggest you now leave that fixed and concentrate on the Windows settings I mentioned above and possibly the recording source you are selecting in Audacity. BTW can you post a screenshot of the available recording options you see in Audacity?
Tried pasting-no joy. Audacity input device pull down shows all five ASUS STX Record slider drivers plus MS sound mapper. The STX Line IN is selected and Line is selected in Windows record sliders also (sliders at max). I found a spec for the STX input/output at 2vrms max. I am going to look at my source with an Osciloscope and see what the line out voltage is on peaks.