Just in case I'm not the one with this issue with Ripper as I spent a few hours getting it right:
I have two optical drives and simply creating a second docker while changing /dev/sr0 to /dev/sr1 in the configuration didn't cut it out for me.
For some reason, even though /dev/sr1 was effectively mapped to /dev/sr0 in the container, makemkv(con) didn't got the memo. Therefore, drive 0 was still /dev/sr0 and drive 1 still /dev/sr1. At best, I could get my second drive to create an .iso file.
To get around this, first, you need two different config directory, say ripper0 and ripper1. You can leave ripper0 as is but in ripper1, you'll need to edit ripper.sh in three ways:
Change every instance of /dev/sr0 to /dev/sr1
Change every instance of DRV:0 to DRV:1
On line 24 (as of this writing) the grep must be set to look for 'DRV:1,' (note the coma) instead of DRV:1 otherwise the grep on $INFO will return all the information on DRV:10, DRV:11, etc. that makemkvcon will return.
That's about it. Hope this helps some of you.