Congratulations on your first set of measurements. You have followed the guidelines quite well.
HST, each of your front speakers is exhibiting a rather severe issue centered at 80Hz, as you already noted (and as shown below).. The highest priority should be to identify and resolve this issue. While the sub distance tweak may help alleviate the issue, there are several steps you could take.
1. Temporarily change the speakers to large and measure each speaker's response without the subs.
2. Return the speakers to small, output the test tone to the center speaker, and temporarily unplug the speaker. This will measure the subs only (15-300Hz).
These measurements will give a better idea of whether the dip is in the mains or the subs response. Once we have that data, steps to address the dip could be:
- Find a better position for the subs (assuming you have some freedom of placement).
- Make sure the two subs are properly aligned with each other (probably not an issue if they are equidistant from the MLP, and if you use Audyssey XT32).
- Make sure the combined sub signal is properly aligned with the mains (the sub distance tweak).
Can you provide the dimensions of your listening room?