"Latency" option selected but it only shows 1 active channel in stead of 2 on external mixer... why? How do I overcome that?

Hi I am Dede,
I am running algoriddim djay pro windows 10. I have selected “Latency” and the external mixer options for better results and sound. I have configured the laptop’s sound card to “quadraphonic” but only one channel is active in the mixer. I also use the external sound card (behringer U-Phoria UMC204HD) for best and reliable sound. PROBLEM: Only one channel is active in the mixer in stead of two. On the other hand if I do not select the Latency option in the DJ Pro sound configuration I have both channels active in my mixer, but the sound quality and reliability is affected. What is your advice for best results with latency option checked in ?
Many thanks.