XDJ ZX w/ CDJ900 NXS - linked via Ethernet cable. tracks played on USB drive on CDJ don't show as played on XDJ XZ

I use 3 decks when DJing so I link a CDJ900 NXS to my XDJ ZX via an ethernet cable and and rca cables.

I export my playlists from Rekordbox to USB drives to play music.  

Is there a way to link a USB drive plugged into the CDJ900 NXS and play that music on the XDJ ZX? 

And... is there a way to play link a USB drive plugged into the XDJ ZX and play that music on the CDJ900 NXS? 

Last time I tried this the audio via RCAs came through, but the Link functionality it didn't seem to work.

As a work around I had to plug one USB in the CDJ900 NXS and another USB into the XDJ ZX and just slected USB on each unit... However if I played a track off the CDJ900 NXS it would not show the the track as 'played' on the XDJ ZX, and vice versa.

I played a 5 hour set and i'm pretty sure I played a couple of tracks twice because of not being able to see which tracks I had already played on the CDJ900 NXS. 

Any thoughts, help, advice, updates much appreciated. 

Thanks!

If I plug a USB drive into my CDJ900 NXS, there is no link button on the XDJ ZX to access the tracks.