Greedo’s subtitles are part of the video track, so you don’t need to worry about that.

Open the MKV in tsmuxer and uncheck everything except the video track and the mono audio track. Make sure the “demux” box is checked, set your output folder, then hit start.

When it’s done, you should have a xxxx.264 (I think - the video) and an xxxx.dtshd (for audio) as separate files. Clear everything out of tsmuxer and load these two files into it. This time, instead of checking “demux” you’ll check “Blu-Ray ISO.” Run it again and you should end up with a functioning BD ISO file.

Note that you’ll need 3x the amount of HDD space as the size of the MKV file, unless you delete the MKV after the first (demuxing) step, in which case you’ll only need 2x the amount of space.