low volume dvi sound

Not sure where to post this,
i made a friend of mine a Kodi box for christmas (Openelec). and i told him to get a dvi to hdmi adapter and a mini jack to R/L audio cable.
He tells me he had audio without the audio cable, and i checked it. Apparently this was added later to dvi.

The only downside is that the sound volume is very low, any thoughts?