Can't get 5.1 sound

if the sound is coming from your monitor, and the 5.1 system is a different system, then can't you just turn the sound on your monitor down? and then have the 5.1 sound on?

That's simply incorrect. The Xbox One has output surround sound since its release-- DTS and 5.1/7.1 uncompressed multichannel PCM over HDMI. Until the last update, it did not support outputting a compressed Dolby Digital bitstream, which is what is needed
for optical (because optical can't carry uncompressed 5.1/7.1). It does now, however.

OP, it sounds like you are selecting 5.1/7.1 uncompressed, which is not supported by TVs (that is for a receiver (AVR))--and that is why you can't select it when HDMI is set to Auto. Most likely your TV is just seeing it as 2.0 (stereo) audio. You need
to set the Xbox One audio to bitstream with Dolby Digital encoding. Even then, please be aware that very few TVs pass DD 5.1 from an HDMI source out though the optical out. What you may end up getting is virtual surround sound, not true discrete 5.1.

I have a 5.1 dolby digital receiver/dvd player hooked to xbox one with an optical cable and to the tv with hdmi Xbox setting is set to bitstream out dolby digital and I get full 5.1 on games and blue ray works perfectly and menu sounds but any music or
video app or a dvd that has 5.1 audio won't work the music and video apps only give 2.1 and the dvd with 5.1 sounds so muffled I can't hear I have tried everything and all I can get is this or fake surround and I don't want fake surround if all the apps are
in 2.1 why wouldn't the Xbox be smart enough to mix the sound through all the channels of audio if the program only does 2.1

An optical cable simply can't pass 5.1/7.1 uncompressed, only HDMI or multichannel analog can (the latter of which the Xbox doesn't have). As such your headset (presumably optical) does NOT and cannot support 5.1/7.1 uncompressed. Instead it supports 5.1
Dolby Digital (DD=compressed), and virtually creates 7.1 from the 5.1 through processing (optical can't pass 7.1 DD+ either, only 5.1). Currently, the Xbox One cannot output Dolby Digital 5.1 over optical, which is why you do not get surround sound in your
headset. It is also not surprising that your TV is not handling 5.1/7.1 uncompressed properly, as that is something you really need an audio receiver to handle. What is probably happening is your TV is downmixing the uncompressed 5.1/7.1 to some sort of stereo
(2.1?), resulting is loss of some audio channels. The rest you hear as"virtual surround sound" created by your LG system.

The solution for you is to get a proper audio/video receiver (recommend Onkyo or Denon) that has HDMI inputs, can handle uncompressed 5.1/7.1, etc.; OR wait until the One can output DD 5.1 over optical, When the latter happens, keep in mind that most TVs
will NOT pass DD 5.1 out over optical. Perhaps yours does (some Vizio models do). If yours doesn't, you will never get true DD 5.1 (just because you hear sound from all speakers doesn't mean you are getting true DD 5.1) from your current setup and would need
to run the optical out directly to your LG system, instead of through the TV. Hope that helps.

February 2015- This is kind of crazy but it worked for me. I was not getting 5.1 out of TV through my XBO but I WAS getting 5.1 from movies and games.

In the XBO menu I switched the audio to "Stereo" from 5.1/7.1 and now I'm actually getting 5.1 sound. Makes no sense but give it a shot.