Still no success with 64-bit drivers. One thing I noticed, that if I open the device once with working 32-bit drivers, after that the 64-bit drivers/software works as long as I dont unplug the usb cable. When opening device for the first time with working drivers, dmesg shows usb-disconnect-connect ...

I had the same problem in Gentoo Linux. Few post earlier attached libps2000.so.2.0.zip helped with my older 32bit Gentoo installation and I get it work with my other 64bit installation when I use 32bit version of drivers in /usr/lib32 folder and compiled PS2000con.c with -m32 option.