Help me guys

I have a Yamaha MG10XU mixer
 
And
komplete audio 6
 
Now i want in a track one to be my Yamaha MG10XU, Picking my vocal signal as a stereo.
 
And
Track tow my komplete audio 6. So it pick a stereo signal from my Yamaha s970 keyboard.
 
So in that case i can record multiple track as a stereo simultaneously?

I have never used that and looking at the spec it is only a 2 in 2 out USB device so you might be able to record 2 mono channels one panned hard left and the other panned hard right.  But sounds like time to read the manual. 
 

I have the same mixer. Yes, you can do it but you'll have to route the vocal mic (and only the mic, not the s970) to the Monitor output and send the mixer's monitor output directly to a third input on your audio interface.

You can record as many tracks as you want simultaneously. Just make the tracks hot for recording and choose the input source for each track.
The number of inputs you can record is only limited by the input channels of your audiointerface. SONAR does not limit.
 

Are you asking for help with setting up your audio interface to work in Sonar or are you asking for help routing to your audio interface? 
 
Peace!
 

11Dreams
Are you asking for help with setting up your audio interface to work in Sonar or are you asking for help routing to your audio interface? 
 
Peace!
 

Both, in sonar asio show me the Yamaha mixer with only with stereo and both left and right as input. so i can't record multiple track as an a stereo at the same time. So i think and trying to connect tow interface at the same time. but i get distortion signal. i search in YouTube i fund it maybe the problem from clock or something. I'm new in this stuff i really need help

As I know, with normal ASIO drivers you can only connect one audiocard.
I think you have to use WDM to connect two audiointerfaces. 2 audiointerfaces at the same time is not very stable.

In a different manner - I route the outputs of one AI on my desktop into two inputs of my main AI on my laptop, effectively giving me tracks from both AIs.
If I desired I could run all individual outputs, I believe there are 6, into main AI inputs giving me all of desktop Al's tracks plus all other main AI inputs.
I do this routinely without problems. But it takes two computers.

Your Yamaha will use the same Stienberg ASIO driver my bands Yamaha mixer uses,, I guess. Its actually a real good driver. possibly the same one used for the Stienberg U series interfaces. 
In the track input dialog choices you should have
Yamaha ASIO left
Yamaha ASIO right 
Yamaha stereo 
 
But I wonder why you want to use that when it makes more sense to just plug your mike directly into your audio interface? The pre amps are probably the same quality so nothing is gained from using the Yamaha mixer. The interface has the audio intputs for both your mike and your stereo keyboard. 
 
Your Keyboard has USB output, does that not send the audio from the keyboard,, or just midi?  It also has DIN midi jack and your interface as well sports DIN midi. 
There could be the option of recording midi and then turning that into something much better sounding using Sonars VST's.. that would be my chioce. You could record both the audio and the midi too. 
 
Note- only one ASIO device can be used at a time so you are better off to leave the Yamaha mixer out of the picture. You could use it to add 2 more channels using WDM mode if your recording a band or more people at the same time. That's how I use mine. 
 
My choice with what you have would be to use your Interface. 
Plug the Vocal mike into CH 1
The Keyboard into 3/4 on the back
And also have the MIDI either USB or DIN hooked up. Not sure if full performances from the keyboard are transmitted as multi track midi but my guess is it does.