No sound in the CUE output

Greetings.
I’ve been using the 1R/1L RCA output from my U24C sound card, connecting them to my amplifier.
Now I added a pair of active monitors to the 2nd RCA outputs 2R/2L and discovered that there is no sound coming from these outputs. I tried connecting my amplifier to the 2nd output instead and still no sound. What am I missing here? I thought the point of these dual outputs was to be able to have 2 pairs of speakers. Isn’t it? :woozy_face:
Greatful for any suggestions :pray: