Actually I tried something today which did not necessarily solve the bass problem (slightly reduced) but improved the sound quite a bit (at least to my ears). As one of the guys suggested, I threw some large cushions in towards the back of the speakers - at the two corners of the room. Created a board platform resting on four large rubber door stops (saw on you tube that some guy used big thick cutting boards to place the floorstanders on top of the same). Placed the speakers on top of the platform with the spikes going in side 4 more rubber doorstops.
As for the furnishing, the room actually has large shelves on the back wall with my CDs and Vinyls. There are thick curtains covering half a wall, one rug, a double seater leather couch and center table.
Glad you saw the post, glad you're getting somewhere with it now.
Another trick is to find a mirror (might need a friend for this) sit in your seating position and get your friend/other half to stand on the sidewall moving along it till you see the corresponding speaker reflection (right wall right speaker) Obversily keeping the mirror level not skewing it toward the speaker.
Place something large and soft their (where the reflection is) cushion or other, do the same on the other side.
Keeping the cushions behind the speakers.
Should help massively, though I doubt you'll get rid of it entirely.
I have no idea what other the guys are talking about with the room reflections, Its called standing waves and its what EQ systems try to elevate with slight delays and other cleaver math things.
If the Speakers are at one end of a room and your at the other all your hearing is nearly 100% reflected sound. It's a simple experiment with a sink of water and stone, just watch the ripples. The ripples will not hit the other side (seating position) without being interrupted If dropped near the boundary and thats 1 stone!(speaker is the stone) The only way ripples/waves do not interact with one another is if the stone is dropped nearer the centre, hence the further you move the speakers out the less the room interacts, dropping 100% down maybe to 90 or 80% reflected sound. But at this point, you also run the risk hearing no sound (nulls!) depends on the size of the room and timings as the waves will cancel each other out at certain points (these are the intersecting points of the wave).
Boom is propagation ie waves all hitting the same point at the same time leading to an increase in volume BOOM!
Speakers excite rooms in different ways depending on where placed. To hear nothing but the speaker the room either needs to be large, non-existent, heavily damped or the speaker needs to be placed near on centre of the room and you with them. This is called the Cardis theory
Don't get me wrong though you're still hearing the tone of the speakers, it just changed slightly, think of it as game Chinese whispers by the time you hear it something has been lost or something has been added.
You'll get there though, I know you say you can't move the speakers but even moving your seating position and inch or 2 can make a massive difference and the same with the speakers, It really doesn't have to be massive movements