SPA-941 Sound Quality isuuses on Asterisk?

I’m using:
1 Server Asterisk 1.2
8 Linksys SPA941 phones
1 PRI T1 digium
1 FXO4 digium

the Server & phones are running on a seprate network (cables & switch)

BUT… I’m suffering from echos, white noise, delay, etc…

Is there any manual for optimaiztaion of SPA941 working with Asterisk ?
:question: :question: