Raspberry PI 1 B no 5.1 sound

I have a Raspberry PI 1 B with LE 8.2.2.

I have some videos with e-ac3 sound that my sound system can't decode (only 5.1 pcm, ac3 and dts).

how can i set up LE so that e-ac3 sound is converted to 5.1 pcm and then sent to my sound system?

i have tried setting the number of channels to 5.1 in audio but then the dialogue (center channel) is not being reproduced.

thank you.

if i try setting number of channels to 4 in audio i get pcm, but i think it's only 2 channels and the sound system plays it on all speakers. i'm even willing to install raspbian but i don't know what tests to perform to see if i can get 5.1 pcm decoded from e-ac3, any suggestions?