To clarify ..
The port in the Sony's is resonating at a certain frequency in the mid-bass .. It's creating a hump in the mid-bass frequency response of the system ..Now that you have the 8's, which are also undoubtedly ported, and creating their own frequency response bump, but at a lower frequency, plugging the ports of the Sony's with a dense foam could smooth out the mid-bass ... Not difficult, just cut an old couch cushion (or any other Dense foam) and push it into the port... listen to some drum and bass music and decide which way that you like it..
And I was expecting that raising the crossover point would probably be part of the experiment ..
(And you can do it with an old sock if you object to slashing up the couch)