Compare your '4x50' headunit to a 4x50 amp. First, the headunit is much smaller, and it has to have all the headunit stuff, as well.

Then, check the power. Best case, 200 watts takes about 14 amps (14.4 v, 100% efficient) while most headunit only have 5-10amp fuses

I'm not saying that headunit manufacturers lie, but...

Toby