itzikr
Hi there,
Thank you for your feedback.
Do you access your NAS server over SMB or DLNA?
If you access your NAS over SMB, you should be able to find the external subtitle files as long as you put the video file and external subtitle files in the same folder and give those files the same file names.
If you access your NAS over DLNA, probably you can't find the external subtitle files as DLNA doesn't support external subtitles.