USB interface under Win7, 64bit and usb problem

I have been asking this all over the place, but only just discovered this forum. I will try to be as brief as possible. Sorry!

I have an oldish Edirol UA-3FX, but a similar fault occurs on an M-Audio fast Track USB.

Acer 5536 Laptop, 4GB AMD RM-74 processor. Works perfectly with Vista 32 using asio drivers into Audition and Reaper.

Swap hard drive to one with Windows 7 Enterprise 64-bit, with the latest bios and all the current drivers from the Acer website, and the 64-bit Win 7 drivers installed for the Edirol.
Plug in Edirol and play audio. Dreadful breakup of sound, slow movement of level meters etc. Put in a USB2 hub with or without power supply between Edirol and laptop and playback is fine. All this is using the asio drivers.

Now, without the USB hub, playback is still terrible. Now go to Win 7 Control Panel, Sound. This Window has tabs for Recording, Playback, Sounds and Communications. It shows the Realtek on-board interface and the WDM drivers for the Edirol.
Hit the Recording tab. The sound becomes clean. Hit playback, sound unusable. This can be repeated ad infinitum.

I've investigated with Microsoft's Xperf diagnostic tool and a USB sniffer (until its trial period expired) These both show that the usb is fine when the Recording tab has focus.  But with the Playback tab when the problem is present, the cpu usage drops but becomes more erratic, and the USB data changes from regular ISOCH_TRANSFER to repeating short blocks of CONTROL_TRANSFER +  ISOCH_TRANSFER.

I'm continuing to investigate, but would be really interested if anyone else can see (or not see) the same problem. As far as I can tell Desktops don't usually show the problem, but I think some other laptops may.

I have done all the normal things such as disabling almost everything in Device Manager. The Microsoft forums push me towards this being a mainboard chipset hardware problem

Any other suggestions gratefully received.

Apologies again for the length of this.