Using Kodi as a NAS/media streamer

Here it is, I have 2 android boxes (one for the living room, one for the bedroom) with CoreElec installed on both. The one in the living room has all my external drives (containing all my movies) connected to it.
I want to be able to use the living room one almost as a NAS to send video to the CoreElec kodi in the bedroom.
So far I've tried SMB and UPNP to stream the video. When I try watching a movie in the bedroom, video plays for a while then starts buffering. No joy.
Any ideas?

Thanks for any help in advance.


Edit: both boxes are Minix U9-H, hardwired to my router.