Here how the stereo option works:
Indpendent Mode : The left signal is processed with Cabinet 1 and the right signal with Cabinet 2. You can position each of the resulting signals with the pan knobs.
Blend Mode : Both signals are processed with each Cabinet. The volume knobs of each cabinet are linked. This time you can position each of the resulting signals with the pan knobs.
It comes with different GUI : two made by me and one made by ThexBucket from GAM.