Nick, I'm not familar with your mobo or the Sandra utility, but it sounds like it is giving you useful information.
Before changing any settings you should backup your system, and in particular your data/SATA drive. Once you have verified backups, you can experiment with your BIOS settings within some level of protection. But first you should document your BIOS settings, so you can recover from any obviously wrong setting that causes your system to become non-operational.
Generally speaking however, you should be ok with making subtle changes, one at a time, then gauging the results. It is important to make only one change at a time, then test immediately to gauge the result. It's also a good idea to reset the previous change before you make another change. This will keep the results meaningful. If you get in too deep or become lost, you can always reset the BIOS back to a 'Default' configuration. Usually this will be a stable configuration, but not necessarily the highest
stable performance that the system is capable of. Worst case would be that you might somehow hose everything up, and have to rebuild your system, reinstall your apps, and restore your data. Sometimes this isn't a bad thing, but you definitely don't want to go through this unless it is absloutely necessary.
There may be some known issues or other mobo config tips if you do some Google queries. Here's one I used:
http://www.google.com/search?hs=Qzg&...gs&btnG=Search
I don't build DAW's on a daily basis, although I am in IT up to my ears. The fellow from ADK has a good handle on tech support specific to DAWs, Nuendo, etc.
Happy troubleshooting...