Exactly. The Camera control panel can ONLY connect to an Atem.. And The Atem embeds all controls into the SDI return to control cameras..
When you use other video mixers often users choose to buy a cheap atem with SDI output. ( Like a old Atem Television studio or a TVS HD..
Then loop the SDI signal from your other mixer into the Atem. And PGM output of the Atem to the camera chains..
Need a GPI Tally box to link the other mixer and Atem to run Tally in sync with your other mixer..
It's designed as a system. If you break that system it wont work anymore. So you are bound to use an Atem.
And no it wont work on the Atem mini because it doesnt have SDI outputs. And the Bi-directional converter will only give you 1 channel output instead of all data..
The only other option if you want to skip the Atem part is Skaarhoj RCP's But the cost of those will surpass the Atem option very quickly..