Here are some things I'd be thinking of trying if I were you (you decide if any of them are practical for you)...
Front L and R, I was surprised by how low these were going, but now I see why. It is beacuse they are right in the corners. I'd try positioning the front L and R just to either side of the cabinet and slightly infront of the cabinet. This will give as much space as possible to the side walls. This should flatten the bass response a bit, meaning that you will need to set the crossover higher (hopefully it will match closer to 80Hz).
Centre channel: Someone already said this but it could help to bring it right up to the front of the cabinet. Also raising it up and angling it slightly (as you said) could help.
Carpet will help, (hopefully also damping the floor resonances you mention).
Can you pull your sofa away from the rear wall at all? (Even just a foot or two may help).
If you move the front L and R you will probably also need to move the sub. First place I'd try is very close to the front corners of the room (I'd try both). You can also try setting the sub level slightly higher than audyssey wants it in the pre-calibration setup. This may allow Audyssey to get it flatter across a wider range after EQ.
Crossovers, definitely start at 80Hz for the fronts, consider changing the surrounds to 100Hz or even 120Hz. The measured response makes it look like your speakers go low, but I wouldn't be surprised if the distortion is quite high at those low frequencies, and this distorted sound gets boosted by the corner placement.
Hopefully the sound may be cleaner with less boomy bass if you can bring the speakers away from the corners.
Once the room reinforcement of bass is tamed a bit you may then prefer Dynamic EQ to be enabled.
I hope you will enjoy the voyage of audio tweaking that you are just embarking on!