Comment 142 for bug 1516025

https://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/plain/sound/pci/hda/patch_realtek.c

 [ALC668_FIXUP_DELL_MIC_NO_PRESENCE] = {
  .type = HDA_FIXUP_PINS,
  .v.pins = (const struct hda_pintbl[]) {
   { 0x19, 0x03a1913d }, /* use as headphone mic, without its own jack detect */
   { 0x1b, 0x03a1113c }, /* use as headset mic, without its own jack detect */
   { }
  },
  .chained = true,
  .chain_id = ALC668_FIXUP_HEADSET_MODE
 },

the simplest way is

1) remove 'headphone mic" fixup from ALC668_FIXUP_DELL_MIC_NO_PRESENCE

2) remove node 0x16 "headphone'

3) add subwoofer pin

{ 0x16 , 0x411111f0 },

{ 0x1a , 0x90100111 },

recompile hda driver