I just noticed you're talking about v8, not 8.5... Wasn't v8 the first to support Win7? This might suggest that X2 is more refined and will work better with Win7x64. Or it might not.
Anyway, some suggestions:
- Make sure you do clean installs of Windows and Sonar - not an upgrade. Some folks have found a world of difference in stability just by reinstalling (ie. Having versions 5, 6, and 8 simultaneously installed can work - but can also cause problems).
- nVidia cards have caused issues with some Sonar users. Make sure you have the latest drivers. (Of course, you should do this with the BIOS and all of your hardware. In some cases, you might need to "roll back" to more stable versions).
- PC optimization. Do it. Disabling Speedstep, FW networking and onboard audio in the BIOS has made a difference to some users.