Can’t get my sub to work:(

I bought some Adam tv5 speakers and I have them plugged into the L R ports on the back of my focusrite 2i2, and they work great:) I have an old sub that I had been previously using with an aux cord that plugged into the back of my computer, but I don’t know how to get the sub and the Adam speakers to play at the same time. I went to guitar center and the guy gave me a cable to plug into the back of my sub (red white auxiliary ends) to the headphone jack of my 2i2 and he said that I should be able to control the volume of the sun with the headphone volume knob but nadda.

I’m still relatively new to ableton, and I can’t figure out the audio settings or what I need to do to get it on… can anyone help me with this? PLEASE AND THANK YOUUUU!!! 🙏🙏🙏