Have any of you ever run 2 MOTU 896HD's together?

If so, tell me the secret.
 
If I hookup one it works fine. If I hook up the other it works fine. I'm only going to use one of them for the inputs, no digital conversion being done on that unit. When I tether them together via lightpipe I see signal in the input unit but it doesn't pass the audio to the other one which is connected to the DAW via Firewire.
 
Any ideas?