Well Handbrake worked, and it produced a nearly 16GB mkv file (with default settings) with no sound. And then I merged it with the sound tracks of the iso.

But then I would download the mkv version, which has more sound tracks for the same size.

So I'm not sure if at this point I should demux the output mkv Handbrake made, and compress the video track, and then merge the audio tracks. And somehow preserve the chapters.

*sigh* I think downloading the mkv would be easier, unless someone has an idea.

Thanks for the replies.