Guys, I have to bring in an update regarding the AJA IO 4K:

It IS possible to use all 4 SDI Inputs of the IO4K with different sources..
It's a little trick or workaround how to tell Catalyst what is what.
First of all: All Inputs must have the same Resolution and framerate, e.g. full HD with 50fps
Now the AJA is set to get an Input Signal of 3840 x 2140 via 4 Quadrants (means over 4 SDI Inputs, each representing a Quarter of the Picture)
In Catalyst you can set now for every input a different quarter and got 4 different SDI Inputs running for this...

Just to let you know

Best

Rolf