Weird Vista Ultimate x64 USB Issue

First Up, my rig:

Mobo: EVGA nVidia 680i SLI
Memory: 4x1GB DDR2
Video: 2x nVidia 8800GTX 768MB (matched pair)
CPU: Intel Core2Quad 6600
PSU: ThermalTake ToughPower 700W
USB Devices:
1) Matrox Triple Head2Go (attached to rear ATX header)
2) USB Mouse (attached to passive USB hub)
3) Epson V200 Scanner (attached to rear ATX header)
4) Passive USB hub (attached to rear ATX header)
5) Microsoft Zune dock (attached to rear ATX header)
6) HP iPAQ hx4705 dock (attached to rear ATX header)

Now, the behavior:

Basically, I dock both my Zune and my iPAQ and I hear the connect tones from the OS and they both show up as USB devices and sync okay. Then, later, I undock both and take them with me. When I return and put them on the dock, neither is detected by the OS. There are no "device detected" tones or anything. The computer simply thinks they're not there. Plugging a USB flash drive into any port on the PC at this point has the same effect -- it's like no device is there at all.

If I restart the PC (literally, just a restart -- I don't cycle the power), then Windows will see the devices and the process starts over.

For what it's worth, power save features are entirely disabled. The machine stays running at full power all the time and never hibernates or sleeps.

I am using the latest nVidia mobo drivers and the nVidia 177.35 video drivers due to a limitation with my TH2Go.

Any ideas on what could be causing this?

I have a similar issue with my HTPC and the Soundgraph iMon VFD. It will lose itself after a while and come back after a restart. Annoying as it's also the IR receiver for my remote

I've also disabled all power management but nothing seems to resolve. Even re-installed Vista to no avail.

long shot... but try removing the USB host controllers in the device manager (dont tell it to remove the driver) and then have it re-detect them.