You can use a y cable splitter, which you can attach to one of the stereo's regular RCA outputs. As long as you have an unused output on the stereo, a cable like ths will work.
http

/www.amazon.com/Belkin-Audio-Cable-Splitter-1-Mini/dp/B00004Z5CP/ref=sr_1_7?s=electronics&ie=UTF8&qid=1391794717&sr=1-7&keywords=y+adapter