Java3D 1.6.0 is more robust than Java3D 1.5 as it relies on JOGL which contains numerous renderer quirks with no equivalent in the buggy native renderers of Java3D 1.5. I don't see how Java3D 1.5 could work better as OpenGL was used by default in it in some cases and the Direct3D renderer was by far the most buggy part of Java3D.
It's open source, you can look at the code by yourself, we use the fixed pipeline everywhere. Maybe there was a small misunderstanding.
There are other means of testing Java applications on a Mac but under different operating systems and I remind you that there are numerous free of charge GNU Linux distros you can install. Sven succeeded in installing Debian on a Macbook Pro 3.1, I'm still trying to install Mageia on the same machine, rEFIt and rEFInd are helpful. You can install Windows on a Mac with Boot Camp, can't you? This excellent tutorial in French
might be useful. It's logical that we don't have to fix Parallels' bugs but please post a comment on its forum and we'll try to cooperate. As I said in the past, it crashes on the very first OpenGL command, it's still the same than with the older pre builds, we can't make it work without the help of Parallels' team.