synchroning two 828mk3 interfaces via firewire ??

[mici]

Hi
I have two 828mk3 interfaces and placed it via firewire serial to the computer.
computer - firewire (1. mk3 - in) - firewire (out) - 2. mk3 firwire in
In cuemix and windows vista I have two windows (#1 and #2).
I set the clock source to mk3#1 internal - it's right ???
If I connect only one interface, I can use ist all ok. With both interfaces I have trouble, no output sound from the computer in any variations ??
Help to the right settings please.
- Windows Vista -

Mici