From the JDA Labs site "RCA Output - RCA output jacks at rear, 3.5mm output and USB jack at front. Black endplates. 95mm case length. Note: The ODAC supports only 1 output; do not use 3.5mm and RCA jacks simultaneously"
Note they indicate NOT to use the 3.5mm and RCA jack at the same time.
I have (2) of the ODACS, one for standalone apps and the other integrated into an enclosure with the O2 Amp.
I use the RCA stand alone version to use in a 2 ch speaker system,