Sorry I've cross threaded a little and answered some of your points in my thread in the Win 7 Forum.
Yes I downloaded all available Toshiba Drivers for Win 7 64 bit from the Toshiba Archive Support site. All 4 of them. The rest came from Microsoft, Intel or Realtek.
The machine had the problem before I restored Vista 32 bit which was running very slow and flaky, often hanging. Now I cannot detect any issues with Vista either on SFC scannow, disc check, Surt tool or device manager - all devices working properly (when present). The audio controller is not shown in Device Manager when booting up cold and the sound icon showing a red cross in the sys tray.
I created a separate partition onto which I have installed Win 7 64 bit. This suffers the same cold starting problem. I don't think these two systems are sharing any drivers, because they are on separate partitions on the hard drive? The Win 7 installation is now running without any reported faults on CheckSUR.
I like the idea that a mechanical connection somewhere is not making good contact. Where to start looking is the issue?
The external sound card you flagged up looks cool. If all else fails......