2 x XDJ700 + RekordBox and Pro Link - iMac 2010 Core i3 - High Sierra

I simply want to connect 2 XDJ's, recent purchases, to RekordBox and play the tracks from the Mac with no USB keys.

I am getting E-8309 Link access errors when I try to load tracks, if I connect even a single XDJ to my managed 1Gbps switch (I've tried HP/3Com and Cisco) along with RekordBox running on my Mac (export mode).

If I direct connect the XDJ to the Mac, there is no problem.

I have run wireshark on the Mac to look at the traffic and noticed a few things:
1) The media transfer uses fragmented packets - is the system trying to use Jumbo packets?
2) The XDJ's use auto IP (169.254/16) - I guess they can't use DHCP?

My main question:
Do I just need a "crappy" unmanaged switch to make this work?

Thanks :-)