The current pre-release of the client ("pioneer" in the version) is only compatible to itself. So you can only play with other testers. Please be aware!
I played without sound and didn't get a single crash. I read somewhere that it might be possible to solve this by installing the game on a slower disk. Maybe I'll try that at some point (didn't have a free disk today) - for now I'd say the problem is solved as it works when sound is disabled. Thanks for the help!
Best,
Step