No idea how the NAS could fit into this, but I have seem similar behavior from VLC on my desktop connected to my marantz amp. By default, the VLC player outputs to the default sound output of Windows 10, so it should work. But it doesn't - silence. But from troubleshooting I discovered that if I go to the VLC menu option Audio - Audio Device, and select the specific device (instead of it being on Default), suddenly it works.
Never got around to troubleshooting it further and have been relying on this workaround anytime I use VLC on that PC.
Never got around to troubleshooting it further and have been relying on this workaround anytime I use VLC on that PC.