Thank you for your answer! But (as you may expect) i'm not very amused by it...
There are quite a few document going around explaining how Analysis for olap can use BW and SSAS datasources....
So for anyone reading this in search of the magical radiobutton for activating your SSAS datasources:
Please discard what you have read about SSAS connections up until know and stop trying. It is a waste of time.
Tammy; Once again, thanks for you quick answer!