Well, I do have an OBNE Blender which could use if I wanted to do A-B on the fly.
But I'm not necessarily expecting them to sound identical, but rather do I like their sound; in that case simply plugging from one to the other and playing a song should be a valid approach.
As far as real use, I'm considering running my Rickenbacker stereo and really I just picked up the SansAmp as a placeholder; however, another option is to run 2x mono with the SansAmp doing deep and the Ampeg doing grit.