1 cu. ft. sealed is going to have a Q of .9. Yellow is the O-Audio with the default Hi-Pass filter at 17.7 hz. Green is the 500 watt amp with the default HPF at 30 hz. Both models are slightly over Xmax.
You can't eliminate the HPF, the sub will bottom out. You can lower the HPF on the 500 watt amp which will take less power to reach Xmax and you end up with the same output as the O-Audio 300 watt amp.