Hi Mate
If passthrough wasn't working then the workaround would be to set it to auto which would then utilise their onboard MAT decoder and send within a container, as you say this could cause lag on some setups.
This issue isn't unique to LG TV's though and I have read countless reports of LPCM not working with other Samsung kit such as here:-
us.community.samsung.com
we have another example here showing LPCM passing fine to the Sonos, but not to the Samsung Bar.
The common denominator in all this is Samsung. I am therefore inclined to point the finger in that direction.