. . . . behringer 12 channell mixer to samplitude . . . setting my mixer with samplitude.....so far i can only get a stereo commection....
Without knowing which Behringer model you have and taking a guess that it is a XENYX X1204USB , then the stereo connection is what you will getin Samplitude - this goes for all mixers which offer a stereo output.
If the Behringer has a surround sound output then IIRC you also need to have a surround sound audio card/ chipset in the PC enabled with the correct number of speakers attached and surround sound in Samplitude enabled.