Floorstander or bookshelf?

I am using MA RS6 with Nait XS in similar size room. My speaker placement is closer to the sidewalls and front wall than yours. At first I found the bass to be a little excessive, but I put the foam plugs in the rear ports. This cut the boominess. Now bass is more natural and well balanced. One thing that probably helps in my particular room is that I have 11 foot cathedral ceiling.
I have also found that the MA speakers are a nice match for Naim gear, after playing around with speaker placement.
The other speaker line I would recommend is Harbeth.
Are you using the foam plugs?

BTW, I also agree to make sure what you have is tuned in optimally before changing.

>I did not make any treatments.The speakers are placed 5ft.(1.5m) away from the side walls and 1.3ft.(0.4m) in front of back walls with 6.5 ft.(2m) distance between them. I find the bass to boomy for my tastes.

As expected. You're going to pickup substantial gain below 110Hz plus whatever you get due to the listener's rear-wall proximity which is also shorter than optimal.

A short-wall placement with the same speaker separation would make things better.

If you can't do that, a shelving high-pass filter would be a fine idea.

Some speakers (Revel makes a few) have a boundary switch which does this.

>What do you consider that should be more appropriate for my room , a bookshelf or a floorstander?

In-wall. Your speakers aren't far enough off the front wall (about 5') for their front-wall reflections to be perceived entirely as reverberant field, aren't far enough out to develop sound stage depth that you'd loose by going with in-walls, and moving to in-wall speakers will eliminate baffle diffraction effects.

Note that by 'in-wall' I mean speakers with well-braced high quality enclosures that mount in the walls (Triad?), not decorator approved units which rely on the resonant dry-wall cavity.