As all we know, (Galaxy S8 & S8+) only has one speaker at the bottom, thats why the sound output is quite underwhelmed when compare to other latest flagships from HTC or even Apple iPhone 7 which using its earpiece speaker as secondary output
Coming from that concept, this mod will allow you to use your earpiece as second speaker as well, creating pseudo-stereo output in result and should give better experience inplaying any audio
if you need help, check my XDA thread : https://forum.xda-developers.com/galaxy-s8/themes/stereo-sound-output-mod-s8-s8-root-t3604613
otonieru@xda-developers 2017