6093 Buffer errors (detailed info provided)

[nucelar]

Hi,
I keep getting Buffer errors (mainly -6093) on one of our PT systems. I could rant for hours about wasted time troubleshooting, but I just want to know two simple things
a) What the hell is wrong with my system
b) How can I solve the problem

Symptoms are:
6093 errors appear randomly on playback. Sometimes a big session with lots of plug-ins and video runs just fine and sometimes a simple session with one mono file will give The Error. Sometimes the session runs for one hour and then stops, sometimes it won't even play for ten seconds.Copying the session folder to another drive seems to solves the problem sometimes.
Trashing prefs and databases temporarily fixes the problem, again, sometimes. Rebooting. Reinstalling... The buffer keeps underrunning again and again. Every day.

Mac Dual G5 2 x 2 Ghz PowerPC
2,5 GB DDR2 SDRAM
OSX 10.4.2

Digi 002R (with replaced harness) connected to front Firewire port
PTLE 6.9.2 cs4 w/DV Toolkit
002R externally clocked to Rosendahl nanosyncs via SPDIF
Rosendahl MIF for MTC to LTC conversion
Buffer Size set to 1024, CPU Limit 95% (tried various settings)
Waves Native Pack v5
Elemental Audio InspectorXL

2 internal SATA drives (160 and 80 GB)
LaCie d2 Extreme 250 GB connected to rear FW800 port
G-Tech G-Drive 400 GB daisy chained to LaCie via FW800

Sony J-30SDI (DV out) or Canopus ADV-100 connected (one at a time) to
rear FW400 port. Connected through an active FW hub for more cable lenght.
We are NOT using the video out through fw option, we output the video through a second monitor.

Am I taxing the FW too much?
Will installing that SIIG FW400 card solve the problem?

Thanks