Interesting topic - plugging bass ports. I just got an Energy S8.3 sub given to me in leu of a debt owed and thought I would try it in my system to augment my CAMs (as I had no sub). It's a ported home theatre sub, so I wasn't expecting the nice tight integrated bass that Louis' subs are famous for. Attack on the notes and percussion was good, but the overhang was not good - too slow and a tad boomy. Admittedly, it takes a fast sub to keep up with any Omega.
I had some 4" thick high density gray foam kicking around (the type found in high end camera cases like Pellican) so I cut out a 5" disc to stuff into the 2.5" bass port - nothing ventured, nothing gained. It made a major difference, really tightening up the bass and eliminating most, if not all of the overhang. Until I can afford a 12" short throw sub from Louis, this should get me by.
A good piece of music to use to hear if the sub is synchronized with the speakers is Yello, Goldrush. It'll tell you immediately whether your sub is dialled in.