Until today I got no feedback from any Mac user.
Finally today one Mac User with java 6 tried it and reported problems to me back. My thanks goes to dora.
Problem seems to be not only that java 6 is not so easily available on Mac and also not used as default jvm by jUCy, but that carbon is 32Bit only which gives jUCy a double ko by requiring 32 Bit and 64 Bit at once.
As cocoa port that will work with java 6 on Mac will take more than half a year at least to finish and be available for 64Bit systems I am now looking if I can do some workarounds.Still the problem stays finding something that works (cross compiling, other jvms) is hard without a mac.