FW connection clicks and pops

[Astia]

This morning we got a FireWire card for our new Mackie DigitalXBus200 console and I‘m having touble getting a clean signal from DP. Depending on the settings there are click either on the FW channels or on the light pipe channels.

Here is our setup:

G5 dual 2,27G w/4G ram
OSX 10.4.4, DP 4.61
Apogee BigBen as master clock
2408mkIII (3 x light pipe to DXB inputs)
fire wire cable to DXB

I searched Unicornation and found great tips once again from qo. The audio from FireWire was horrible before I changed the HBM to 4 and Work priority to low as he suggested. I tried different disk read/write & buffer size values but still some clicks appear.
I was supposed to do a proper testing before using the FW card routing for out clients but the temptation was too big and we are just starting to mix 2 bigger projects.
This problem can also be a non-DP-related but all tips are more than welcome.

Thanks in advance