Short Version: I love the port plugs. They made a huge difference.
I did some experimentation with household items and had good success so I ordered the Axiom port plugs. I felt they were overpriced when ordering, but it turns out they are pretty nicely engineered.
I have M80's and I always wondered if I would have been better off with 60s. I have them in a medium to small room and one is in the corner.
Plugging the bottom ports have done wonders. I have more detail in the mid range and cleaner bass.
I purchased two pairs so I could fully experiment. Plugging both ports doesn't work well in my set up. Detail is good, but you can tell something isn't right.
I have a set of M3s, I will try some experiments with those and my "extra set".
I listen to my system everyday. I watch the same scenes from movies all the time so I have references. I use Ratatouille, The Incredibles, and Kill BIll Vol. 2 the most.
It was easy to hear the improvement.
Watch Andrew Welker's video and see if they might help you and do not hesitate to try them.
My favorite Incredibles scene for sound reference: The music while Robert is working out followed by his visit with Edna. (Good video reference too-lots of blacks and whites at Edna's house).
Ratatouille: The stand up bass of the mouse band during the welcome home celebration and Ego's review.
Both movies are filled with so much to listen to.
I like Kill Bill Vol 2 for the dialog in the wedding chapel at the beginning of the movie.
M3 and Manley Stingray
M80 and Pioneer SC 55