I had a Motion Sound Pro-3 and it only sounds it's best when played loud. It has to push the air. When it does ... LOOKOUT ! It's awesome, but it pales by comparison to a good stereo setup because you are separating the sound flow by speaker placement.
One on one, the rotationg horn sounds MUCH better than the psuedo processor in the kb, but the conditions have to be equal. Stereo amps, widespread placement etc.
The internal processors are pretty good in many situations. Best to detrmine if you need the ultra realism or the compact setup.