Adding .sub subtitles to OGM file

[ShinHyuga]

I'm kind of new to encoding OGM files. I used Oggmux to add 2 audio tracks and subtitles. But the subtitles were in SubRip (.srt) format.

I have an OGM file that already has 2 audio tracks. The subtitles are in a .sub (VobSub?) file (and another file, a .idx).

1. Can I either add the .sub subtitles to the existing OGM file?

2. Can I convert the subtitles from VobSub (.sub) to SubRip (.srt)? (And then use Oggmux to add the .srt subtitles?)

3. Is there any way of demuxing the 2 audio tracks from the OGM file?

Please help!
Thanks!!