New XPS (8900) -- no stereo audio for stereo speakers

I have no audio, but when I go to (right-click sound icon in tray) --> Playback Devices --> Playback tab --> right click "Speakers / Headphones Realtek High Definition Audio" --> Configure, then in Speaker Setup dialog:

* If I select Quadraphonic in the "Audio channels" list, I hear sound for the RL (rear-left) and RR (rear-right) speakers, with my stereo speakers plugged into the black jack in back. I cannot get sound when testing the regular L and R speakers in Quadraphonic mode; I've tried all 5 jacks.

* When I select Stereo, then clicking L or R speaker icon to test results in no sound, again no matter which of the 5 jacks i plug my stereo speakers into.

* So the only way I have sound is in Quadraphonic mode, but only for the back speakers. Therefore I cannot hear regular stereo output from applications, such as Youtube in Chrome.

This seems like a bug, or a highly unintuitive aspect of Realtek's or Dell's software at best. Any ideas on how to solve? (Beside buying full surround sound speakers)