Can't record stereo

Hi and good morning to everyone.

I recently purchased an external mixer (MCI 500). I am trying to make the mixdown through it, but when I record it into cubase 7.5, only the left side is recorded, or, if i pan it to the center, it records a mono signal. When I do this through two analog inputs from my soundcard (mr816x), the problem appears, but if I record through spdif , being previously converted by an external AD, it records the stereo file perfectly. Where can be the problem?? Thank you in advance.

Are you sure you’ve set up the inputs correctly in the VST Connections window (F4)?