Topic: FF800, Sonar and Windows XP

Help. I'm at the end of my rope. I've been using Sonar for 20 years (yes, started with the DOS/MIDI only version!). About a year ago I bought a new RME Fireface 800 and am using that with a Dell Studio XPS i7 chipset 12 GB RAM Windows XP 64-bit machine, along with Sonar X and 8.5. Folks - every session I have ends up with a system lock up. I have to reboot. If I didn't save just before the lockup, data is lost of course but I am usually on top of saving and don't lose much. But it is insane that this won't stop. I have the latest firmware for the RME, the latest drivers, etc. I have tried just about everything. What do you guys think - is there any .ini file that i need to look at? Is this a known issue with RME and Windows XP 64-bit? I hope I don't have to go to Windows 7... I want to make music not screw with computers... every other aspect of my set up is stellar.
thanks!
doug