Thanks for the suggestion. I have tried around alot now and unfortunately none of my attempts work. When I do a system rest (at any place in the program) both sensors return wrong values. Actually, the first sensor shows the same constant values as the second sensor (see previous post for the values). I also tried to instantiate two classes (one for each address) in the global scope, before the setup and loop routines, but no success.
I really think of buying a multiplexer now.