I've been dealing with this issue for a few months. In our studio we have two Evolution 75s, three 54Hs and one 54M. We upgraded the work stations for these cameras to new MacPro 2.66 Quadcore computers running Snow Leopard. We have the same crashing problems that you are experiencing with our Evolution 75s under CaptureShop 5.6.3 and 5.6.4. However, the 54Hs and the 54M work fine. Which leads me to believe that it is a Firewire driver issue. The 54s use FW400; the Evolution 75 uses FW800. Just a guess.
We have come up with two options to deal with Evolution 75: Use Exposure 7.0.3 with 10.6 or install 10.5 on the new MacPro and use Captureshop. It is possible to downgrade the operating system from 10.6 to 10.5, because the latest generation of MacPros was released running under Leopard. All you need to do is get a 10.5 install disk for a MacPro 2.66 Quadcore. We were lucky that our IS department had one. But you can get one from a local Apple repair facility. Just re-install the system from it. Everything works perfectly. We even re-installed the 10.6 system after downgrading to 10.5 to make sure that we could do so in the future if and when Sinar corrects the problem. THE EVOLUTION 75 UNDER 10.5 and CAPTURESHOP 5.6.3 OR 5.6.4 WORKS VERY WELL.
The other option is to use Exposure 7.0.3. It has great potential! However, there are some issues with it. First the positive: it is rock solid -- I have never crashed it; color profiles are excellent and match Captureshop; and it is fast, utilizing multiple cores, which CaptureShop does not. BUT, here are some of the problems with it. The live video focus is very poor without an LC shutter (although I have not used it with and LC shutter, but Sinar implies that is is better with the LC). It is no where near as good as Captureshop video focus without LC shutter. Exposure does not auto open exported files in PhotoShop. You have to go the folder that you exported the files to and open them from there. Not a big deal, but tedious. And it does not seem to hold most settings from shot to shot. Fortunately the default output profile is very good and matches closely CaptureShop's. But there are some other canned profiles to choose from which are very good and useful, but they do not hold shot to shot, so you have to remember to re-select. Another annoyance. Finally, you must do a lens plus sensor shading reference every time you start the software or you can get center fold lines in your files. This, fortunately, seems to hold from shot to shot.
It's not a perfect situation. We have opted for downgrading to 10.5.8 and CaptureShop 5.6.4 for one Evolution 75 and 10.6.2 and Exposure 7.0.3 for the other. Mostly because of the photographers' preferences.
Good Luck.