Using two different cabinets that are placed a bit apart would be the best way to get the stereo effect. But, using a typical amp, you will have the same tone coming from both outputs. So, again, no difference in tone (unless different speakers are used in the cabinets). Even then, your effects wouldn't be true stereo, because the amps outputs aren't stereo, each are mono sending the same signal. The best thing you can do is use a wet-dry rig. To do this, you would run your amp like you normally would (amps output into 1 cabinet). Then run the amps line out, or effects send, to a stereo effects processor and run it into a stereo power amplifier out to two more cabinets (wet) which are placed on the left and right side of the "dry" cabinet. This can be a supper sweet sounding setup, but can get quite expensive and complicated quick. Eddie VH uses a setup like this live.