The Windows XP PC 32 has no problem communicating via its native serial port, but can not communicate via the COM port (Prolific) of the cable (the other PCs have no native serial port).
According to the datasheet on the site Prolific, settings supported by the PL-2303 driver are fixed speeds "classic" ([...], 1800, 2400, 3600, 4800, 7200, [...]) so too far from those I seek to attain.
It seems that the Prolific driver could be customized, and the cable would be able to communicate at different speeds; However you should contact Prolific and it seems to be more a process than an integrator of end customer.
I'll point me to the Belkin F5U103 deemed operate at speeds that interest me, unfortunately 3x more expensive, and obviously not exempt fault (Driver for XP newest 32bit).
Update: after having done extensive research (on Russian forum ...), it turns out that it is possible to set some specific speeds via a value in the registry ("ExtBaudRate" in the key Prolific the driver). It should however calculate a value through a certain formula a bit long to describe here.
Search for "383385600Hz" in google and take the result of website nexia-club.ru translate possibly ...
I added a star because the cable can now meet my needs. I would have put 5 stars if it had done without the need to search for this information at the bottom of the web ...
