Since MKVs do not play PGS SUPs I convert them to idx/subs and rather than remux them I just make sure they are in the same folder as the MKV and they have the same name(as per the Seagate manual). Except for the fact that the Seagate will freeze when presented with 1080p idx/subs it will accept 720p or dvd subs generated by BDsup2Sub without a problem.

The subs have to have the exact name as the MKV so is there a way to have more than one sub in the same folder with what the WD or Segate thinks is the same name. I've tried using (), _, .., Gr, En and track. None of them work. Is there something else that might?