Issue connecting the DDJ-FLX4 to a Speaker

I have been trying to connect my DDJ-FLX4 to my Bose Soundlink Revolve+ speakers and have not been successful (I am using Rekordbox). At first, I tried connecting it through Bluetooth. The problem was that when the speaker was working, I could not listen to any songs through my headphones. Therefore, I bought an RCA cable but now it just plays songs through the computer while the speaker makes one loud sound. What can I be doing wrong?