USB bus reset troubles

Problem:

USB bus resetting every couple of hours completely rearranging the tree of all connected devices.

Description:

One of our Dells is a Poweredge 860 with 4 USB modems and 3 USB sound devices attached. I configured udev in such a way it translates the USB layout (e.g. 4-1:1.0) to device names in /dev.
Every now and then something somewhere decides to reset the lot out of the blue, completely rearranging the USB tree and messing up the device names. Could this be some powermanagement issue, ACPI settings? Software issue? Hardware? Combination? I've been looking for days to solve this, but still clueless.

Funny thing is I desperately installed an older machine (Poweredge 650) and it works flawlessly.

Details:
- Linux SuSe 10.3
- Poweredge 860
- 3 x Creative Xmod
- 4 x USB <-> serial converter with modems attached

The messagelog looks like this:

Feb 18 17:33:35 voip1 kernel: Uhhuh. NMI received for unknown reason a0.
Feb 18 17:33:35 voip1 kernel: ehci_hcd 0000:00:1d.7: fatal error
Feb 18 17:33:35 voip1 kernel: You have some hardware problem, likely on the PCI bus.
Feb 18 17:33:35 voip1 kernel: Dazed and confused, but trying to continue
Feb 18 17:33:35 voip1 kernel: ALSA sound/usb/usbaudio.c:670: cannot submit urb (err = -108)
Feb 18 17:33:35 voip1 kernel: ALSA sound/usb/usbaudio.c:670: cannot submit urb (err = -108)
Feb 18 17:33:35 voip1 kernel: usb 3-1: new full speed USB device using uhci_hcd and address 2
Feb 18 17:33:35 voip1 kernel: usb 3-1: not running at top speed; connect to a high speed hub
Feb 18 17:33:35 voip1 kernel: usb 3-1: new device found, idVendor=04b4, idProduct=6560
Feb 18 17:33:35 voip1 kernel: usb 3-1: new device strings: Mfr=0, Product=0, SerialNumber=0
Feb 18 17:33:35 voip1 kernel: usb 3-1: configuration #1 chosen from 1 choice
Feb 18 17:33:35 voip1 kernel: hub 3-1:1.0: USB hub found  
Feb 18 17:33:35 voip1 kernel: hub 3-1:1.0: 4 ports detected
Feb 18 17:33:35 voip1 kernel: usb 4-1: new full speed USB device using uhci_hcd and address 24
Feb 18 17:33:36 voip1 kernel: usb 4-1: not running at top speed; connect to a high speed hub
Feb 18 17:33:36 voip1 kernel: usb 4-1: new device found, idVendor=0409, idProduct=0059
Feb 18 17:33:36 voip1 kernel: usb 4-1: new device strings: Mfr=0, Product=0, SerialNumber=0
Feb 18 17:33:36 voip1 kernel: usb 4-1: configuration #1 chosen from 1 choice
Feb 18 17:33:36 voip1 kernel: hub 4-1:1.0: USB hub found  
Feb 18 17:33:36 voip1 kernel: hub 4-1:1.0: 4 ports detected
Feb 18 17:33:36 voip1 kernel: usb 4-1.1: new full speed USB device using uhci_hcd and address 25
Feb 18 17:33:36 voip1 kernel: usb 4-1.1: new device found, idVendor=041e, idProduct=30d0
Feb 18 17:33:36 voip1 kernel: usb 4-1.1: new device strings: Mfr=1, Product=2, SerialNumber=0
Feb 18 17:33:36 voip1 kernel: usb 4-1.1: Product: Creative Xmod
Feb 18 17:33:36 voip1 kernel: usb 4-1.1: Manufacturer: Creative Technology Ltd
Feb 18 17:33:36 voip1 kernel: usb 4-1.1: configuration #1 chosen from 1 choice
Feb 18 17:33:36 voip1 kernel: input: Creative Technology Ltd Creative Xmod as /class/input/input9
Feb 18 17:33:36 voip1 kernel: input: USB HID v1.11 Device [Creative Technology Ltd Creative Xmod] on usb-0000:00:1d.2-1.1
Feb 18 17:33:36 voip1 kernel: usb 4-1.2: new full speed USB device using uhci_hcd and address 26
Feb 18 17:33:37 voip1 kernel: usb 4-1.2: new device found, idVendor=041e, idProduct=30d0
Feb 18 17:33:37 voip1 kernel: usb 4-1.2: new device strings: Mfr=1, Product=2, SerialNumber=0
Feb 18 17:33:37 voip1 kernel: usb 4-1.2: Product: Creative Xmod
Feb 18 17:33:37 voip1 kernel: usb 4-1.2: Manufacturer: Creative Technology Ltd
Feb 18 17:33:37 voip1 kernel: usb 4-1.2: configuration #1 chosen from 1 choice
Feb 18 17:33:37 voip1 kernel: input: Creative Technology Ltd Creative Xmod as /class/input/input10
Feb 18 17:33:37 voip1 kernel: input: USB HID v1.11 Device [Creative Technology Ltd Creative Xmod] on usb-0000:00:1d.2-1.2
Feb 18 17:33:45 voip1 kernel: ALSA sound/core/pcm_lib.c:1717: playback write error (DMA or IRQ trouble?)
Feb 18 17:33:45 voip1 kernel: ALSA sound/core/pcm_lib.c:1717: playback write error (DMA or IRQ trouble?)
Feb 18 17:34:01 voip1 /usr/sbin/cron[10357]: (root) CMD (   /root/voip/voip_daemon)
Feb 18 17:34:05 voip1 kernel: ALSA sound/core/pcm_lib.c:1717: playback write error (DMA or IRQ trouble?)

Anyone had similar stuff happening? Or maybe able to tell me whats wrong?

Thx in advance.