I feel it also dampens the big dynamic peaks in the music. I've done no end of experimenting with the position of my speakers, which if i'm honest have too much bass output for the room they're in. A pair of rolled up socks cut the bass most efectively, but as I say, also constrained the dynamics a bit. If you're not using the port bungs supplied by the manufacturer then contact them and see if you can get some, because they ought to have put in a bit of research or at least experimentation and come up with something that does the job optimally, without unbalancing the whole frequency range. At the moment I'm using the manufacturer-supplied bungs, which in combination with filling my speaker stands up completely and getting the speakers as far from the back and sides as is domestically acceptable seems to have done the job of eliminating the boom, whilst not affecting dynamics too much.
To be honest it's one of those things where experimentation is the only way as every speaker/room/listener interaction is unique. Also try reducing any toe-in (i.e. less angled in towards the listening position), someone recommended that to me and I was surprised to find that that did actually reduce the bass a bit.
Good luck
Dan