In my all too extensive experience of experimenting with my Neats to get the bass under control, I've tried a range of things. Anything (suitable) that you put in the ports is going to reduce the amount of bass, but also in roughly proportional terms impair the speaker's dynamic abilities. I found that bunging the ports with anything reduced the life and energy of the sound, via that reduction in dynamics. In the end i've left mine un-bunged as he disadvantages outweighed the benefits (for me).
In order (from most subtle to most striking), the things i tried were - bunches of straws, short foam bungs, long foam bungs and rolled up socks. The foam bungs were supplied by Neat.
I know it's not always easy to do this and remain within the constraints of domestic acceptability, but changing the position and orientation of the speakers has just as noticable effect on the bass. Moving them away from rear or side walls should reduce the bass, ensure that they are not the same distance from both the rear and the side, and one thing that I was recommended that surprised me, was reducing the amount of toe-in, but if you try that it's obviously a case of trial and error to strike the right balance between getting the image sharp and the bass under control.
Another thing i did which had a really beneficial effect - you coud try this if your speakers are on carpet - was getting some granite worktop savers from Aldi and putting them (2) under each speaker stand. Tightened things up in the bass dept, with a nice side effect being an increase in clarity in the mid-range too.