I know you’ve made good decisions and are on the right track for attaining better overall system performance and enjoyment. Here are the things I suggest for best results:
1. Position each sub precisely in the room, and in relation to your listening seat, utilizing the ’sub crawl’ method. You can google it for details but I’m willing to describe this effective method if you have a lack of results.
Hopefully, the perimeter walls in your room are free of room decor, or can be rearranged, to allow positioning each sub along the perimeter of your room walls to achieve the best sounding bass at you’re listening seat. It's difficult to predermine exactly where each sub's optimum position will be, you're ears will be the deciding factor and even a few inches difference will result in the bass sounding better or worse to you.
2. ’Bass can be "localized" at about 80 Hz’ means that humans are generally incapable of determining where sounds or musical notes are coming from when their frequencies are below about 80 Hz but we’re very adept at determining where sounds or musical notes are coming from when their sound wave frquencies are at or above about 80 Hz. You’re correct, this is due to the perceived directionality of sound waves in direct proportion to their frequency.
3. The goal is to set the level and crossover frequency controls on each sub as low as possible with the bass still sounding good to you: powerful, dynamic, smooth, fast, detailed and natural. This is really a matter of your preferences and will likely be the most time consuming step in the setup process. I recommend recruiting an assistant to slowly adjust the controls as you determine optimum settings from your listening seat.
4. Best midrange, treble and stereo imaging results are typically achieved by placing bookshelf speakers on stands that raise the tweeters to near ear level when you’re seated. They are then positioned in the precise room positions, and in relation to your listening seat, that results in the optimum perceived midrange, treble and stereo imaging performance. Moving the speakers a few feet away from the wall behind them also typically results in better overall performance. This, again, is a matter of personal preference.
These are the main points I thought would be useful but I’ll post again if more come to mind.