Can you tell me the specific Unifying device you had success with?
I know I've used the K800 keyboard. Not sure of the mouse model number. I find very little stuff that won't work, but occasionally something won't work like cosair keyboards.
Its an active USB->PS2 adapter and they are not cheap. Its not just some pass-through thing. Its similar to this:
https://www.startech.com/Server-Management/KVM-Switches/PS-2-to-USB-Keyboard-and-Mouse-Adapter~PS22USBI also have a Logitech wireless PS2/USB optical mouse I use with my minimig. Its probably going to be hard to find but the part # is 810-000154