MIDI not passing through outputs

[berth]

Hi-

I am fairly new to more complex midi setups, so it's quite possible I am doing something wrong here. 

Setup is:

• Novation Summit (local off and transmitting on CH 1) MIDI OUT -> 880 1 IN
  
• Polyend Tracker MIDI OUT -> 880 2 IN
  
• 880 1 OUT -> Summit MIDI IN (receive on CH 1)
  
• 880 2 OUT -> Hydrasynth Explorer MIDI IN (local off, receive on CH 2)
  
• 880 3 OUT -> Korg Poly 800 MIDI IN (receive on CH 3) *I am not sure how well this old synth will work with my desired setup
  
• 880 4 OUT -> Polyend Tracker +
  

Assumptions and observations: 

1. The Summit will be used as a MIDI controller to play notes on any of the above output devices
   
2. The Tracker will sequence the synths connected to the 880 Outputs
   
3. I have SUMMIT IN 1 and 2 linked to all four outputs
   
4. It works with only the Summit (local is off, so it has to be getting the MIDI notes from the 880) 
   
5. None of the other devices seem to receive the MIDI data
   
6. I have tried it with and without Chan Split
   
7. I have tried changing the output devices receive channels to ALL/OMNI and specific channels
   

If I plug the Summit directly into one of the other devices, the MIDI data gets through fine and notes are played with the Summit acting as a MIDI controller (have not tried with the Korg yet, but the others work)

So I am wondering if there is some key piece of knowledge I'm lacking, or my routing is incorrect, or if there is an issue with my 880. I just bought it brand new, FWIW. 

Any help would be much appreciated!

Thanks in advance!