I put a spare WD red 4Tb Hard Drive formatted Ext 4 inside my HTPC and uploaded some videos & music to it
Comparing NAS Stream to the internal HDD
With the internal Hard Drive:
Video appears better, eg: 4K has more clarity with better depth & slightly better colour & sharpness
Sound in video is different, loud action noises, etc are clearer & louder, where as vocals are a bit subdued by this
Audio is also better, HD music definitely has more punch in bass & high treble is slightly sharper and clearer
NAS: OMV 3.0.99 wired / intel G3258 / Asus Z97K
HTPC: LE 8.2.5 / intel i3-7100 / Gigabyte H270M-D3H
GTX1050 to 4K OLED / STX Essence to Aktimate Mini