I'VE GOT AN ANSWER, I NEVER IMAGINE I HAD AN ANSWER FROM ROLAND :
I phoned to ROLAND FRANCE (of course I'm french) and... I have a reply : the chip in the SYB-5 is less expensive because it's a chip used in others products, and the chip in the SYB-3 was made only for the SYB-3.
that's it : they made lots of chips -> lower cost -> SYB-5 cheaper.
and they also said that the SYB-3 is out... there are still some SYB-3 to sell, but it's the end of the production now...