Well, as all of you predicted, things seems to get better:
The first time I've put on the JH13, they didn't sound good with the EQ and other effects off. So I turned on the EQ and effects as I do with the E4c. This is how I got the initial impression that opened this thread.
Following your recommendations, I've turned EQ and other effects off. This time the general feeling was better, but the mids felt like they are hidden behind the lows and highs (this was very apparent and not much fun). Then I've put the volume few notches up from what I'm used to, and that was it !! Everything was balanced, and the bass was so beautiful that I couldn't stop listening even though my wife was waiting for me. I never thought of myself as someone that will say "beautiful bass", but that was exactly the words that came to my mind when this bassy part was playing...
Now I'm quite confident that as all of you said, as time passes on I'll enjoy the JH13 more and more. Just hope to be able to do it with low volume levels.
Thank you all for your comments !