If the front left and surround right work with other sources (the internal test tones could be a good first test, but a calibration disc with individual channel test tones played via digital input would also be a useful check of the situation), then the problem can be traced back to the 7.1 Direct input or before it. You could swap left and right fronts and left and right surrounds at the 7.1 Direct input to see if the inactive channels move to the right front and left surround - if they did, that would eliminate the 7.1 Direct input as the problem. You could also try swapping out the left front and right surround cables for different cables, just to be sure that there's not a bad cable in the mix. If none of that uncovers a culprit, then we'd need to look more closely at the source...