@qasimrox
well the power rating of amplifiers is done differently, what do you thing a speaker rated at 400 watts take 400 watts at 12volts... no this aint the case.......
and in voltage conversion basic law of power is taken in account i.e p=v*I..(p=power, i=current, v=voltage)....
now you are taking 660 watts at 220volts... this 220v is also rms(root mean square), let us leave this and consider somple 660 watts. if the invertor is ideal (ehich is impossible) than also on 12 volts you have to dish out 660/12=55 amperes... ehcih is a lot of current my brother....
i'll explain all the audio wattage levels and ac/dc wattage levels later more elaborately ....