Rekordbox 6 - External Hard Drive - Mac

Following the release of the Pioneer RX3 I read somewhere it only works with Rekordbox 6 and not 5 so I'm thinking it's time to make the move. 

I DJ with USBs / Hard drives so just use rekordbox to export to them.

Porting my library from 5 to 6 was easy but my external hard drives will not work with DJ Players (tried with CDJ2000NXS / NXS2). 

Does anyone know what I am doing wrong? They are formatted as FAT32 and show up fine in the Rekordbox software. My Mac OSX on 10.13.6

I can't seem to get this working so any help is greatly valued!