Proac 3.8 or Sonus Faber Cremona

The Concentra and the Proac 2.5's or D15's sound great together. But it might help if you share why you want to change speakers. What are you looking for that you don't get with the EAII (which BTW,I also love with the Concentra)?

The principal problem its a lack of bass output efficiency.
Another problem it's when i'm listening to the system during night and i can't go to high in volume then the sound looses only bass output.

I would recommend a musical sub like REL or Vandersteen if everything is great except for the bass ouptput at lower volumes. The vandersteen 2wq sure helps me with my PROAC 1.5's at lower listen levels and even higher ones.

I think Fletcher-Munson has a role in what you're experiencing. Other than a separate subwoofer, as Aniwolfe suggested, allowing you to control the bass volume separately, or a tone control, I don't see a solution.

I also hazard to guess that the one thing that we rarely do, but should, when auditioning speakers is turn the volume down. Many speakers have a tendency to sound balanced at a certain volume "sweet spot" but colored at lower or higher volumes. Try it when auditioning your replacements.

Good luck.

I recently sold my ProAc 3.8s as I am planning on upgrading to the new ProAc D80. I listened to to the Sonus Farber Cremona today at a local store and was simply blown away with their smooth life like sound. I can't say that they are better than my ProAc 3.8s were but they are extremely musical (and this with with a Plinus SS integrated amp). I do prefer tubes however and used an ARC VT-100MKII with my 3.8s. The Cremona has spiked my interest to the point that my local dealer is going to let my take a pair home for a week for audition in my system.