For alienware which also use alc668 but with headset, headphone and mic jacks
there will be no auto mic selection since you have headset mic and mic jacks
what you need is
fix the headset mic pin and disable the headophone mic of model dell-headset-multi
decide which output pins share volume control since you have headset, headphone, speaker and subwoofer but only three audio output/volume controls
For alienware which also use alc668 but with headset, headphone and mic jacks
there will be no auto mic selection since you have headset mic and mic jacks
what you need is
fix the headset mic pin and disable the headophone mic of model dell-headset-multi
decide which output pins share volume control since you have headset, headphone, speaker and subwoofer but only three audio output/volume controls