Many thanks.
Finally I use the same Hyperlobby folder and I needed to open Hyperlobby in 2 different Windows sessions with the -i parameter. That allow 2 different folders in users/ApplData/Roaming
...
Many thanks Fojtasek for this old but very useful link It answers to one of my questions: Le server AND the client have to set the same speed. I use actually SPEED=10000, perhaps with actual good ...