I'm running AirVideo HD Server 1.0.14 on OS X Mavericks. When the option "Force hard subtitles" on AirServer HD is switched on, font support is missing for ASS subtitles.
Screenshot of VLC on OS X:
Screenshot of AirVideo HD on iOS 7.0.6:
AirVideo HD: the text is rendered with a sans-serif font which seems to be the default font used when corresponding font is not available.
Please look into this issue.