1) It's "current", not "amperage".Running multiple amps drops RCA amperage more than RCA voltage correct?
KelvinI am not sure you will be able to tell from the manufacturers specs, but by tearing them down or looking at the schematics as I do everyday, more and more radios are doing this to save money, instead of building a high end pre-amp section with its own power supply to get the high output voltage. Its much easier and cheaper for them to steal it from the high level output signal from the audio ic.
The problem here is that anytime you increase the signal, aka increase the voltage or power, and then reduce it again, noise filters into the equation. Also audio ics are well known not to have the high fidelity that you want for SQ. So its not as clean of a sound that a nicely done pre-amp voltage section has, thats problem number one. Problem two is that you have amplified the signal to 20 volts or higher thru a less than ideal set of electronics them you are buffering the voltage back down thru a cheap set of resistors to get the voltage down to the usable line voltage of say 3 to 8 volts. This adds noise, takes away dynamics. It's just a nasty way to get what appears to be a high end signal very cheaply for the manufacturer.
Almost all of your radio manufacturers are going to this on low to middle level units to save a buck and to give the lower end audio customer what he thinks is a high end feature. Your better, high end radio units will still be true preamp sections producing a very clean high voltage signal.
they don't all sound like shiz. which onesw have you listened to? i can tell you some of the first classd amps sounded awesome. there is some that had power supplies that were not quite as responsive to the output, giving a little bit of a muddy output with the fluctuations on music, and then there is bad signal processing, but that's the manufacturer, not the class d faultIs that why they sound like $hit?