Nbox has the ability of showing subtitles (ssa/smi/srt files) but only in Chinese and English (!!!).
Download AviAddXsubs (http://www.calcitapp.com/AVIAddXSubs.php).
Then use it to import subtitles to the video file (then you can delete the srt file)
Then watch the video on Nbox but don’t forget to enable the subtitles from the remote control of the unit.