RCA ouput for Yamaha audiogram6

So i want to know how to proceed for making my Yamaha audiogram6 sound card output go to my mixer in one channel in in RCA, Because the Audiogram6 has only 2 phono output which are connected with 2 powered monitors speakers, L and R. and i haven't any powered speakers, I use a mixer with 2 channel and which is then connected to my speakers.

So i try to do :
a 2 RCA Male to 3.5mm Stereo Male, which is connected to my MIXER (One channel only the RED one) with a : 1 RCA Male to 2 RCA Female Y Splitter Audio Adapter, and finally the I connector to convert the 3.5mm male to 1 phono streo male to go the the audiogram6 output on L speakers out, I did the same thing to the R speakeres out but so far only one speakers playing..
You need to use both channels because you are working with stereo. Each channel has different information. If your sound card has left and right rca outs, you shouldn't have any problem. The easiest thing to do is split the signal right at the sound card. Try something like this: Monster IHP Y-2F MKII. If you do a search for it on amazon there's a good picture. You would need 2.