DRB,
I'll take a stab at it.
Jumper 1 - This is the setting for whether or not you want the coupler/repeater to repeat signals that it has detected have already been repeated by another device. The CR234 has circuitry in it to detect that. How you set that will depend on your envirnment. I would say to say to put the jumper on. If you get an issue with too many repeated signs causing an issue, then turn it off.
There are also 8 dip switch settings you can change.
I would leave these on the default settings (OFF). These are for envoking some of the special features of this coupler. A detailed listing of what all of these mean is in the instruction sheet that comes with it.