I didn't have much luck yet, but it may be me not making correct connections too. I don't think I know how the connections should go between TV and soundbar and then to amp. I do see LPDM on the WiiM app and it thinks it's playing but I hear no sound. Swapped HDMI's around between Arc and other inputs.
My Directv box only has one hdmi on it connected to an HDMI port on the TV. ARC out of tv to soundbar. That part works. I tried soundbar to amp and tv to amp but just thinks it's playing but no sound.
Life would be simple if a HDMI splitter could work between Directv box and WiiM amp. Are splitters, ok? I was able to use coax out from STB to Amp and that worked but had to put a converter in the mix and more wires in the mix.