The, what I like to call, "flee Market" makers, are ususally the flashy looking "light parades" that are bright, with polished chrome and carry names like Duel, Audiobahn, Legacy ect.ect. The idea that these manufactureres rate their own products with these skewed specifications are very misleading. Any headunit made at this point will say maybe 50 watts rms Xs 4 channels. Why then would someone buy a (lets use my latest amp, as i am going to upgrade soon) 50 watt times 4 channel plus 300 for the sub, making it a 5 channel amp, then  pay this money for an amp of the same "rating" as my head unit? First lets look at size alone, the amp in a headunit is only a few inches big, literally, verses the amp, which is 18X9X2", you can see right there that the amp manufacturer wouldnt make it that big if they didnt have to. Included in the size is the heat dissapation. Amplifiers create alot of heat when in operation, and by design are always full open, and stay that way, when you use the volume control, you are "gating" the output signal... it is a lot more then i can into with my limited knowledge, but the idea is that the way amplifiers operate, its inherant for the to dissapate heat, another reason for there size, due to the heatsink size and material.(differs amp to amp and quality of manufacturer) Now to the power side, headunits have small gauge wire going to them, example my AVIC_Z2 uses something along a 16 gauge power wire,(one that is unswitched) where the amp uses 4 gauge, more then 4 times thicker! but the both have 50 x 4??? Again, I do not know how they skew these number exactly, but it is obvious that 50 watts by JL Audio, or Blade, Mcintosh, even Eclipse or MTX are more impressive, louder, cleaner, with more headroom, and higher db ratings and more importantly giving you the frequency responses in both lower and higher numbers the you will ever get with lesser amps and headunits for power. I hope this helps anyone wondering if they should buy an amp that doesnt say 1800 watts! verses the on that cost twice as much with a much more realistic RMS rating( not peak) of 100X2 but with much better power switching and freq. response. those amps that are all about their high power ratings are usually garbage and should be avoided at all corners. take care good hunting -  Bruce L.