HDMI 1.4 is limited to 10Gb/s which maxes out at 4K/30. You aren't going to be able to pass anything higher than that through the Anthem.
If the Anthem supports ARC, then that is DEFINITELY the way to go here, or use the optical out of the LG to the Anthem. You will be losing Atmos and HD lossless, but the Anthem wouldn't get that through ARC either.
The problem with 4K/60 or higher is that you have to have ALL compatible equipment, not just some. EDID will force the lowest common denominator of HDMI to be used otherwise.
Here's a nifty chart that shows resolutions and the bandwidth they take up...
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