Firebox - Sound slows and distorts - Help

First my system specs:

Compaq Presario SR1911X
AMD Athlon 64 processor 3500+
2.20 GHz 960 MB RAM
Windows XP 2002 SP 2

Nuendo 3.1.1 Build 944

I have updated the Firebox firmware to v 2.46.
I have set the processor scheduling to background services.
I have disabled windows sounds.
I have disabled all windows visual affects for best performance.
I have installed the 1394 patch at
I have set the power scheme to always on.
There is no wireless card in the computer.
The firewire card is the only card in the available PCI slots on the
I checked and my firewire card does have a VIA chipset.
In the advanced firewall settings under "Network Connection Settings"
I have the "1394 Connection" deselected.
Inside Nuendo under VST Audiobay my Master ASIO driver is set to the
Firebox ASIO driver.
Under "Expert" settings in the VST Audiobay, I have set the audio
priority to "Very High."

My problem is this: Sound playback starts to distort and slow down. If
I reset the CPU processing speed on the Firebox from low to high, the
problem corrects itself, until it happens again, and then I set it
from high to low or to medium, and on and on in a never ending cycle.
This problem happens with just one single track recorded in the
project. Say I am listening to playback and I zoom in and out either
horizontally or vertically, bang, I get the distortion and slowdown.
I then reset the CPU processing speed on the Firebox, and everything
works fine until I zoom in and out again. It happens from time to
time when I open the mixer, and I have also had it happen when
previewing a plug-in on a track. I have opened the VST Performance
meter, and I never see any spike on the CPU when I attempt to do any
of the functions that have caused the slowdown and distortion.

I am at a loss. Thanks in advance for your time.