(got the tracking number, the 4520 will be here on the 7th)
You'll find that with REW, you'll have to move the subs to various locations around the room until you find the one that works the best with the acoustics in the room. The graph is also saying the acoustics in your room, likes the right sub in the corner.
In your case, I would suspect that if you leave one in the front right corner and one behind your main listening position, after running XT32 and making the normal changes to speakers on small and the crossover frequency for all speakers set to 80Hz, you'll have a killer graph from 4Hz to >120Hz and everybody here will be envious.
What about the last chart with both Triaxes and Audyssey on, it looks way different. That giant dip is gone
The huge "V" are nulls and is the reason one needs multiple subs so as to sonically fill those nulls in with complimentary sound waves to offset the cancelled sound waves from wall reflections.