How to stop the boom in the low frequencies

I have a pair of Gershman X-1+Sw1 Subwoofers and have them paired up with a DNA 225 Amp. The Preamp is an old Sumo Athena. Although I am satisfied with the over tonality of the system, what really bothers me are the really quick bass lines that tend to hang and make a slapping sound against the walls. I have tried to stick the speakers out into the room, without improvement. What will tame the bass?
Some tweeks for the amp or the preamp? Cones etc...?
Some sound deadening panels behind the speakers?
Some sort of device that simply lowers the registers in the low end?

I need specifics of brands and results,also where purchase them.

It sounds like you are having problems with room resonant modes. This is one of the most common problems in room acoustics. Most room treatment (passive) does not help with frequencies below 150 Hz or so. To deal with that passively you either need a helmohotz resonator or a bass trap tuned at the frequency you are trying to attenuate. The problem with the resonator in large rooms is that it will disapate energy in other frequencies and can create some new problems of it's own. There are on the other hand a few devices (active) that are designed to specifically control these problems. Sigtech, Tact, Accuphase all have digital correction equalizers. Rives Audio will be releasing a purely analog based system that operates from 300 Hz down to 16 Hz. It's 3 band per channel. I founded this company, so I do not want to make this forum into an ad. But I do think this is exactly the type of device you are looking for. More information can be found at Or you may contact me directly through my e-mail here at Audiogon.
Rives: It's appreciated that you do not want to make the forum an ad. Always a fine line between what's acceptable and what's not. But, if you disclose and are upfront, IMHO, its nice to have a professional room/acoustic person in the mix.

Maybe your amp is clipping?

I found this at very low volume levels with certain musik.

Do the room stuff, then, look elsewhere. Email me for my melodramatic story,,,,,
buy this book to understand the problem better...and figure out a fix.

master handbook of acoustics, fourth edition, F. Alton Everest
Clueless: Thank you. I debated whether or not to post. As you say, it is a fine line. Sayas, also points out an excellent resource. We use it regularly.