I'm still nervous about ICH10R. I've just noticed that of the items returned from a search on intel.co.uk only one is a download of ICH10R itself, all the others are returned because ICH10R is mentioned somewhere in the description. And the one and only purely ICH10R download is only intended for server versions of Windows.
But I have had another idea. I found some roughly comparable threads on Tom's Hardware, and on one or two of them people were advised to set up the secondary disk as a 'single disk RAID (0) array'. Example: New hdd shows up in bios but not in disk management - Hard Drives - Storage
This sounds odd. Like going into a bike shop and asking for a one-man tandem. But if someone can confirm it makes sense I'll give it a go. I presume it's something I'd do under cntl-i at startup.