Those numbers are ratings put out by the manufacture to give you an idea of what they claim their product can do.
The way you find out what your max needs or draw on the system would be is to do a test with a volt meter and an AC amp clamp anything else is only going to be a guess.
Volts times amps = watts
Measure the AC volts from the speaker wires
Clamp the positive speaker wire as close to the amp as possible
Multiply the two numbers and you have watts
Sounds simple but there is more to it than that you will need some test tones to get an accurate measurement and you will need to let it roll for a few seconds to get a real number and not a peak number.
Now with music the total draw is always going up and down and what you want to know is can my electrical system keep up with the audio system right?