Contact Dell Technical Support. Explain the issue and troubleshooting we have tried. Tell them to setup a "Part Only Service" to send you the Dell Creative Sound Blaster Recon3D PCIe x1 sound card, part number 0DR8F. Read through the XPS 8700 Owner's Manual for instructions on how to remove the left side cover and install the PCIe x1 sound card.
* Download and save the Creative Sound Blaster Recon3D driver to your windows desktop
* Once you receive the sound card, restart the XPS 8700
* Press F2 to enter the bios
* Go to Advanced
* Go to Onboard Device Configuration
* DISABLE the Onboard Audio Controller
* Press F10 to Save and Exit
* Allow the XPS 8700 to boot all the way into Windows
* Click Start- Shutdown- Shutdown- Ok
* Disconnect the power cord from the XPS 8700
* Facing the front, lay the tower on its right side
* Remove the left side cover by removing the thumb screw
* Install the PCIe x1 sound card into an available PCIe x1 slot on the motherboard. Be sure it clicks into place
* Close the cover
* Stand the XPS 8700 up
* Reconnect the power cord
* Power the XPS 8700 on
* Install the PCIe x1 sound card driver
* Restart the XPS 8700
* Connect the speakers to the added PCIe x1 sound card green jack, the microphone to the pink jack