PA Wattage, Speakers, Ohms, Etc.

[BigJD]

So 600 watts into two 400 watt-rated speakers, for 300 watts per speaker?

And which IPR? The 1600 or the 3000? The specs in the manual listed online are for the 1600.

The IPR 3000 . That'll give you plenty of power for those cabs.
You'll need to use some limiting for protection.