I think another way to approach this is to use something like an Arduino (which does support usb hubs) as a router...
e.g. Arduino <-> usb hub <-> axo 1... axo N
the usb hub, the Arduino could then be programmed to take messages from various axo boards and forward them to others. (depending upon the topology you want).
I like this approach as its flexible, usb is fast, and also can power the axo boards off the hub (also the Arduino too).
I'm doing something similar with a BeagleBoneBlack/Bela, but overkill for just this. its not bad, whats quite nice, is to program the axos, all I need to do is unplug the usb host from the BBB, plug it into the computer, and I now have all axos connected to the computer for programming.