Thank you for your replies and sorry for my incomplete informations.
1. My RME HDSPe AIO is set at 256 samples
2. All the 6 instances of VE are set at x2.
3. The Network is Gigabit on all the machines involved.
4. The connections are done through a ZyXel GS-1116 Gigabit Ethernet Switch
I can add also that I used exactly the same system and exactly the same template with FX Teleport until today without any problem.
I've just decided to switch to Vienna Ensemble 3 only because FXT, which worked perfectly under XP64+Cubase4, seems to have a strange attitude with Vista64+Cubase5 (the same orchestral template I used to work on under Cubase4+XP64 with reasonable use of CPU, under Vista64+Cubase5 fill the CPU and it's not possible to playback at all!).
I thought there were some tricks to disable protocols, services, features to speed up the network.
Regarding the tracks: as you can read from the last point of my first post, if I playback ALL the tracks coming from a single machine, everything is fine and flawless. So all the Strings tracks are fine (slave 2), and the same it's for Woodwinds (slave 3), for Brass (slave 4), for Piano and Percussion (slave 5), for Harps and Chamber Strings (slave 6) and for Solo Strings (slave 1).
Thus, every machine works like a charm, playing back all its tracks without any noise.
The problems start when I try to sum tracks to tracks inside Cubase.
I will experiment more about that.
Thanks anyway.
Luigi.