As it was pointed -prior to any troubleshooting- that theses speakers may not be of my taste, well right now I don't feel the need of building a crossover or such. I'm really pleased with the sound!
Yes it can have been clearer in the mids and a bit too much on "s" and "f" but it does rock! I think it's more an amp question now. Played a bit with a Sansui AU999, nice and round bass, even if not too deep sadly, made it a pleaseure to listen to at very low level. Highs and image are not that clear, my TK2050 amp does it better there, bass are more extended but tighter and/or less present. Will try some more, maybe more powerfull than these 50wpc amps... a TA3020...