This morning I thought I'd do more testing on the other connections on the mount. Especially the USB3 through the mount, and the DC provided power.
It mostly ended up as a shopping list though to get more cables.
While the USB worked through the mount I have not been able to do a proper USB3 speed test to check, especially as I want to connect the ASI1600 this way. I need another USB3 type B connector to do proper testing. Ebay order underway.
For the DC power I did discover something that is obvious from reading the manual, but not so obvious if you just play with the mount.
The main input power to the mount is 12V 5A from the supplied brick (and there are 3 output points on the mount to connect devices that can take 1A). However on the mounting plate at the top there are 2 more output points that take 5A each (I'll need one to take 2A to the camera, the other will go to the focuser/dew heater system). To power these though you need to supply a separate 10A DC input (connection on the mid mount panel).
So now I need to either get another power brick for the 10A connection, or one that can handle 12v 15A plus and maybe some form of splitter cable.
I'll count the above as a minor negative - I should be able to solve it, but realistically, iOptron could easily have provided a USB3.0 cable and a suitable AC power supply that could split to the 5A / 10A 12V DC input.