Comment 23 for bug 1200925

http://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/tree/sound/usb/mixer.c

 /* USB descriptions contain the dB scale in 1/256 dB unit
  * while ALSA TLV contains in 1/100 dB unit
  */
 cval->dBmin = (convert_signed_value(cval, cval->min) * 100) / 256;
 cval->dBmax = (convert_signed_value(cval, cval->max) * 100) / 256;

switch (cval->mixer->chip->usb_id) {
 case USB_ID(0x0d8c, 0x6):
   if (!strcmp(kctl->id.name, "Speaker Playback Volume")) {

you need to overwrite cval->dBmin and cval->dBmax for the Speaker Playback volume

  }
  break;
}

 if (cval->dBmin > cval->dBmax)