I have a new stompXL and obviously cannot connect NIXIE because of the issue above so I bought the box that @CraigGT recommended. I am curious about the routing. I assume it is the following, but I do not know for sure.
STOMP OUT > MIDI Merger IN
MIDI Merger OUT > TIMELINE IN
TIMELINE OUT > Bigsky IN
Then use a MIDI to USB
MIDI USB OUT > MIDI Merger IN
Bigsky OUT > MIDI USB IN