Here is the answer I got. Have not tried it myself.
"The IR IN on the Darblet expects a pin-out, from tip to sleeve of: (3.3V VCC Out, 3.3V IR In, GND). If an external, powered IR extender is being used, a 3.3V IR signal should thus be present on the ring (middle contact), GND connected on the sleeve, and the tip should be left disconnected (because the Darblet is supplying 3.3V there, expecting an unpowered IR extender).
WARNING: Do not mis-connect or apply more than 3.3V to the IR IN port. Some extender systems may operate at 5V, and may thus damage the Darblet and void warranty."
Any IR snake that has these specs should work fine.