I tried playing Mandalorian which has 5.1 audio using FxSound on MPC-BE Player but the volume becomes extremely low as FxSound likely doesn’t load all audio channels except 2 channels, nor enhances 5.1 audio nor sends it to Windows Sonic for Headphones.
Switched back to Realtek HD Audio Manager enabled with Headphone Virtualization, Loudness Equalization, and Windows Sonic for Headphones enabled in Sound > Playback > Properties > Spatial Sound. (For 7.1 Virtual Surround Sound.) Now 5.1 Audio works properly and sends all 6 audio channels to Headphones after processed by Windows Sonic for Headphones.
FxSound needs features like Headphone Virtualization and 7.1 Virtual Surround Sound to fix it.