speakers close to the back wall ?

That Salk Songtowers have a transmission line design, which allows them to be placed 1 foot from a wall with no boomy bass. For less than $3k you can get your own custom wood veneer and upgrade to the RAAL ribbon tweeter.

Go to North Creek Music and check out the Big Kat floorstanders. These and the mini-monitor Kitty Kat are the only remaining models in George Short's "near wall specific" series and are at the top of the line.

George has considered all the design factors that compromise a speaker's performance when it's placed near the wall and dealt with each one of them. With this placement, you won't get a better soundstage than the Kitties deliver and there is no boom. George's work with crossovers is outstanding. I'm gonna sound like a shill if I go on. Do check them out.

http://www.northcreekmusic.com/

Audio Note speakers work well near walls and corners ... also transmission line Jordan jx92 based speakers from Carolina Audio, Konus Audio and AudioWood among others would work well also

Have you tried some absorbing material in the port? A cheap fix if it works.

Some Linns, high end HT speakers, i.e. Thiel SCS, etc.