It means that with a 0 dB tone, each of your amplifiers will produce 500 watts ... The purpose of calculating this information is to prevent clipping and damage to your drivers as this makes it impossible to physically clip your amp ... However, the downside to this is you may not get the desired performance with music, so you may want to modify this method (use a lower sub level (say +10 on a scale from 0-15) or a lower level test tone (say -3 dB)
Decado - Yes, you want to use ~200 VAC unless you plan to exceed 200 volts ...
digital mint, Yes, you want 44.7 volts ...