Comment 6 for bug 1332900

http://voices.canonical.com/david.henningsson/2011/11/29/turn-your-mic-jack-into-a-headphone-jack/

since your alienware have headset and headphone jacks, the two dell models won't works as they are dessigned for those single Jack dell notebook

https://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/commit/sound/pci/hda/patch_realtek.c?id=560b92779cb8748fbf01436b19b1269b6193819b

http://voices.canonical.com/david.henningsson/2014/03/07/headset-jacks-on-newer-laptops/

seem not support retasking headset Jack to line out