Regarding audio on a 3 channel sound bar. Usually all audio is basically the same on L, R, and center channels like it is on BBC 135 right now. The 4K is putting voice on L and R along with some background sounds like birds, etc. The 4K center channel is only doing background sound on my soundbar. On the regular channel 135, it is putting the voice on the center channel along with some background.
NOTE: I have a 1080 TV, but that should not matter with regard to sound.