Well, easiest is to keep the 20 as master and 100 as slave, given this is the way it is already wired / jumpered / configured.

Any results from that "ls /drive1"? I suspect that the directory structure that the player relies on (/driveX/fids) is not there on the 100...

EDIT: Ah. I see you posted while I was replying. Yup. That is the problem. Do this:

rw ; rwm
mkdir /drive1/fids
rom ; ro
reboot empeg
test.