I just joined PC, downloaded all the freebie files, Bryce 6 installers, extra content etc, all up around 1.3Gb of stuff. I have installed B6 and spent all day yesterday transferring over legacy mats, sky presets, obps, tex files etc and testing to ensure they worked okay (99% did).  Most could just be dropped into the apprioriate folders and worked fine. 

I tried to take shortcuts by dragging from Bryce 5.5 directly into Bryce6>Presets>Objects. Some of my obp files from Bryce 5.5 containing a dozen or so objects each caused Bryce 6 to crash suddenly (on Mac) when I tried to creat new object and clicked on the item in the pop-up preset chooser.  It seemed drawing the thumbnail of the object caused the quit?  Anyway, something was corrupt/incompatible. Problem was solved by exporting the objects individually from Bryce 5.5 and reimporting individually into Bryce 6. The objects then load and render fine, textures intact.

I have yet to sink my teeth into Bryce 6 with a scene creation and render. HDRI to get the hang of as well...  I am using Rosetta emulator on Intel core duo Mac and thus am hanging out for the promised Universal Binary Bryce 6.1 release...