Let's review what you have done so far:
-Elimated the headphone as the problem- you tested them on another system. However, since the phones need an extension jack, i would verify both connections (into extension, into headphone jack), I do the sometimes with my DT990's into the Front Port- it requires an extension that I really need to make sure I plug in until it clicks into place.
- The phones seem to have an impedence of 48, which is enough for the ST to drive at it's lowest default setting.
What you have NOT elimated yet (RiceEatin is has touch on these):
- Your computer OS (please tell us what you have- I assuming Windows)
- Your driver set-up (the pic you display)
- The ST card itself.
Suggested Next Steps:
- OS=Is the ST a new install that you just did? If so, you need to do the following: Disable the audio options in the BIOS; use driver cleaner program to clear out any old audio drivers.
- Driver= AFAIK, the ST can only be set-up for either rear(which you are using) or front (FP headphones). So, I would stop trying to connect it through the Z's for right now. If you have a front port headphone, I would try setting up the driver for that first. Once you switch that drop down to FP headphones, you should click on the little play button to test the left and right channels. You could then switch the drop down back to Headphones and plug into the rear jack.
- ST Card= Once you have tested all of the above, it would then be time to look at the card itself.
Please try everything I mentioned above first, then let us know the results.
