10.6.4 had a necessary video card upgrade which was beneficial to the DS interface stability.
The i7 2.0 GHz. was only available on the MacBook Pro, MacBook Air and Mac Mini (2011), the logic board should allow you to upgrade to 16GB RAM, but the only one of these capable of running 10.6 is the Pro, therefore it came preloaded with 10.6.8 and you have these updates already (but you should check for system updates and run them anyway since it does a tremendous amount of background cleanup)
If you would like to expand the RAM, and it’s cheap right now if you can swing it you have two slots for PC 10600 SO-DIMM 204 Pin RAM running at 1333MHz.
8GB RAM (or more) is really going to open that system up noticeably with multiple figures in your projects.
With or without a RAM upgrade and assuming you’ve updated.
• Is your account the system administrator account? If not it should be for stability with DS.
• Have you repaired permissions from Macintosh HD:Applications:Utilities:Disk Utility (repair permissions)?
• Have you created another admin account and tired your sessions in that account to see if they don’t crash?
If the last one works you may have a corruption in your current user account
A reinstall might not hurt either, but reinstall in an admin account and immediately repair the drive permissions.
You can also use any Mac OS from 10.6.8 to the latest and greatest from Apple on any of those 3 i7 macs. I don’t know if DS works in 10.8.x but I think some users reported stability in 10.7. Upgrades for OS are again really inexpensive for Macs.