thanks for the quick reply @LukasPsy, and sorry for my belated answer!
yes, I did try both old and new version. but I found the cause, a rather simple/stupid one:
for various reasons, I wanted to use pygame not pyo and apparently this is simply not included in the standalone version we have installed on our lab-machines (see Standalone Win32 for v1.84.0 doesn't include pygame)
psychopy’s behavior to default to pyo looked to me as if the pref.general['audioLib'] functionality would not work