If you look at the 20Hz to 100Hz range your variation is 77dB to 95dB or about 18dB which is the same swing (different frequencies) that I’m getting on the “before curve” measured by the SVS AS-EQ1 for just the subwoofer in my room. Also, unless I missed a reading it looks like the largest swing from 20Hz to 200Hz is about 25dB from 70dB to 95dB which IMO looks similar in magnitude to what I’m seeing in my room. So I would say that your room is already looking better than mine.
As for what’s acceptable to you only your ears can determine that and now that you are measuring the FR the numbers are also going to start playing tricks on your head. I suggest doing some serious listening along with the measurements while continuing to tweak the existing setup you have. If you have some headphones that are reasonably flat from 200Hz to down below 100Hz that might be a better way to gauge how the FR of your speaker should sound w/o the room in the equation since I’ve noticed using both Audyssey and the AS-EQ1 that a few (+/- say 3) dB improvement here and there is hard to make out under real listening conditions.
Eventually you may want to consider room treatments to take care of the 100Hz to 200Hz range if tweaking speaker/seating placement doesn’t help enough. For the below 100Hz range multiple subwoofers is probably your best bet, and you’ve got a pretty big room so a little extra dB there might also help. Only after tweaking placement and using room treatments and multiple subs would I consider going beyond the EQ already available in your receivers Audyssey. IMO even a dedicated subwoofer EQ system like the AS-EQ1 can’t tame the low frequencies across multiple seats very well. Should know more today on how it performs with multiple subs as Sean is coming over with two of his for some testing.
Like Ken said try measuring with Audyssey off. When tweaking placement turn Audyssey off since it’s applying correction for that last setup it measured. Also, it’s better to find the best placement for you speakers and subwoofer and then run Audyssey. While Audyssey can help some people a lot it works best if you give it as much help as possible.
Hopefully some of our experts on this subject will chime in soon as most of my knowledge on this is still theoretical and several people here have done much more practical application in this area than I have.