How does 3 /4 deck mixing work with VCI-100 & Traktor?

How does 3 /4 deck mixing work with VCI-100 & Traktor?

I was wondering how 3/4 deck mixing works with the internal mixer and Traktor?
I men if one was mixing in deck A/B and those inputs are being used, what to use to bring in lines 3/4? I assume maybe 3/4 deck mixing is only designed for a external sound card…or am I wrong? I am curious of how this is designed to work in Ean’s or others Traktor TSI’s, etc..

You only need one set of outs if you’re mixing internally. Nothing changes. You aren’t using inputs on your sound card. Just load up decks C/D and mix away