If someone still has problems managing named pipes in MT4 v600, this is the way I solved it:
It wasn't between 2 mt4 but between a powershell script and a mt4 that send it's new positions.
As it wasn't time critical and primarily a kind of proof of concept I used normal files: mt4 opens (and seeks at the and) and adds the lines and powershell checks the existence of the file and reads and deletes it :(
I tried to connect to a running (local) socket server (to map in to out) as well but the mt4-socket-client never could establish a valid connection. :(