Anyone try stuffing their ports?

I would have first tried pulling them further out into the room to see how that affected, but they are already pulled as far out as they can be so this is not an option.

My HSU subwoofer, operating on the same principles as all other ported bass enclosures comes with a SINGLE dense foam plug for one of TWO ports.
The sub is provided with a switch for 1port / 2port operation. I don't know what the internal circuit changes entail.
The manual says the switch is for 'Maximum extension mode' and 'Maximum output mode'

Not that it matters, but I run maximum extension mode, since I rarely go to nose-bleed levels.

You have'nt included a full system picture but it appears that your subs are to the outside of your speakers. One tweak that might make a difference is to put your subs inside the left/right speaker position and the exact distance from the listening position.

Saw your system link ( Nice ) . I've had the best luck with the sub 3 to 4 feet further away from the listener than the speakers , seems to integrate better that way . This is of course system and room dependent , you'll have to try it everywhere , which i'm sure you have .

Any blockage of a port will roll off the bottom of your speaker sooner, Your speaker will not go as low in frequency! If your speaker is truly "Boomy", you might try removing the port and replacing it with a longer one. The longer the port, the lower the tuned frequency which will lower the frequency hump. If your port is too long, you will change your hump to a dip. If at at all possible, I really recommend moving the speaker, trying to remove room boundry reinforcement and not mess with the design of the speaker.
But if you must block the port, Material matters on each application, just because a pair of pajamas was ok on one speaker in one room in Australia, doesn't mean the same application will work on a different speaker in a different room in Ohio. The amount of air escaping will change the tuning frequency, so a sponge will sound different than cardboard or pajamas. Good Listening, Tim