Please help - Recording a mix with the DJM 700

im trying to record a mix using my 2 cdj 900s and djm 700 using the software audacity. however my macbook pro 13 inch retina (2015 model) does not have line in for the headphone port, I tried a headphone jack to rca running from my laptop to the record out on my mix and it doesn't work. Some people suggested a headphone splitter but I've read some reviews and it says it doesn't work, just want to make sure whats the best option before i buy something. What is the cheapest option for me that will allow me to record mixes with my djm 700, any help would be appreciated, cheers