Dieter -
I'm not a JRiver employee, but I just did a search on "Dieter" and found nothing.
What version have you been using? If you want stability, stay with the latest "official" release, available by clicking at the top of this page on Jukebox, Download. It is currently 8.0.372. The later versions, such as 8.0.380, are for testing by those who don't mind a few problems. Beta versions of 9 are for those who really want to help out and don't mind occasional crashes.
Now, if you've stayed with only "official" releases and are having lots of problems, then you need to communicate them clearly via this forum. I agree with Xen-Uno that most of the problems are probably specific to your system, because thousands of people are using MJ with no difficulty. When JRiver suggests a fix such as "get the latest audio drivers", try it--very, very often that is the problem.
Stick with MJ--it's worth it.
But don't stick with the Vikings, unless you like jailbird prima donnas that couldn't catch a touchdown to save their lives.
Scronch
P.S. I know you're probably not a Vikings fan, just bear with me.