Honestly, yes and no. The idea behind an amplifier is to take energy and simply transform it. That being said, the reason people use the word clean signal is simply a way of saying a clean steady power supply to the speakers. Any tiny drop or increase in power supply at any time will change the sound quality. That is the reason "high end" amps, sometimes, tend to sound better. In a perfect world, with a perfect DC current throughout the vehicle, then pretty much all amps would sound the same. High end amps usually employ better components like a lower tolerance on their capacitors, inductors, resistors, etc so when the mathematics are projected for varying power levels which every car has, the amplifiers with lower tolerance levels will do a much better job at maintaining a steady signal. Besides different options which may make an amplifier cost more to reduce incoming noise, EMF (which is pretty negligible), or ground loops, most of the cost goes into getting that power signal matched accurately while minimizing the tolerance levels of an ever changing current. That being said, if you have plenty of power to work with (upgraded alternator, batteries, big 3, etc) it may not be such an issue as the amplifier would have a massive "pool" of current which it can draw from as needed require less use of all of the "high end" components which have been added. Its the same reason that some people add external capacitors. A lot of people believe that a capacitor will help with power consumption, but in all reality those large external capacitors simply serve the purpose of maintaining that steady/ smooth signal which we are all looking for. I hope this makes some since, Ive never really tried to put it into words. Lastly, different amplifiers have different ways or steps, as well as a different amount of, ways and steps with which they attempt to maintain that smooth current which may cause a slight difference in the sound. With regards to the "$15000 contest" I am guessing that they did not use an actual automobile. In a car/truck/van, the amplifier is contesting with a multitude of different currents spread across the body, frame, and multiple ground locations. In a real life situation what if for a split second the current was taken from the amp for a temperature change in the A/C or the belt skipped a mm on the alternator; Which amp could handle the immediate change better the high end amplifier or the POS. Even when its just a battery signal changes still occur in the current of a vehicle constantly. I do believe that different amplifiers can sound differently. Ever listen to a song you've heard multiple times and then all of the sudden a note occurs that you never remembered hearing before?