Plug the two RCA jacks at the end of the cable that isn't plugged into the Line/Speaker Out on the Soundcard into the two Tape Input Jacks on the mixer.
Okay. remember those cables I told you to buy? Plug the RCA end of the other one into the Tape Out jacks on your mixer and the 1/8" stereo jack end into the Line In on your soundcard.
How can the stereo aux returns not exist when it says here on the desk they do? I've missed something else haven't I!! God! Learning ancient arabic would be easier than this language of sound engineering.
Okay. I've taken a look round the back of the mixer. What you need is a cable with two RCA jacks at one end and two 1/4" phone jacks at the other (you can get adaptors that fit right onto the RCAs). Plug the 1/4" phone jacks into the Control Room Out sockets on the Behringer then plug the RCA jacks into the Aux Input on your stereo amplifier.
Or plug a pair of headphones into the mixer's headphone jack.