This is now a 15 page thread to wade thru, so it's easy to miss. But there is a workaround to get 'high impedance' 2v output w/o rooting. It's explained earlier, but here it is again:
1. Get one of these:
Josi Minea x 3 Pcs 3.5mm Audio Jack Extender Headphone Adapter with 4-Pole 3.5mm Connectors (3 Ring Jack) for Apple iPhone 6/6S/6+/5S/SE iPad Samsung Galaxy S7/S6 & Most Phones & Tablets [ 3 Pack ]
https://www.amazon.com/dp/B01MTND45R/
2. Then one of these:
FAAEAL Conductor Earphone Impedance Plug 80 220 ohm Noise Cancelling Adapter 3.5mm Jack Professional Reduce Noise Filter Plug (220 Ohm)
https://www.amazon.com/dp/B07FM8GJL4/
Plug the extender in. Plug the impedance plug in. Plug in your headphones. Turn on LG. It should switch to hi impedance. Remove impedance plug. Do not remove extension. Plug phones into extension. You now have hi impedance.
However , I recommend you do not use low efficiency low impedance phones direct. Instead, use a 3.5mm to rca, plugged into the #1 adapter and a HP amp - Atom, Heresy, etc. I use a Liquid Spark, plenty of output to run my HE400I in low gain..
You can also get it to switch to a 1V output simply by plugging a 3.5mm to RCA, connected to your Atom etc. directly into the LG (w/o any adapters/extension). When the LG 'sees' the Amp input impedance, it switches to 'line out,'/1v mode. Most HP amps will be fine with this.