So this sub is 500watt RMS, think of that as like normal playing power. Not peak power. Peak is 1000Watts on this unit.
Ok to answer your question, I’m assuming your amp is 400watts peak, if it were RMS then yeah it would be fine. While it will probably drive this sub at lower volumes I think it will clip/distort at higher volume because it’s undersized. Your 8gauge wire should be fine with your 400watt amp. I have an Alpine single channel 600watt amp I use with this sub and I have either 4awg/6awg tied in for ground and source power.
It also matters if your amp supports 2ohm subs, if it’s a 4 ohm amp it will likely overheat on a 2 ohm setup.