You need to go to Rear Axel / Output shaft, realoem is great but its not always obvious how they catalogue systems.
It looks like the 2.5 and 3.0 are the same part number, the 2.2 has different part numbers so may not be interchangable with the 2.5/3.0
http://www.realoem.com/bmw/enUS/showparts?id=BT12-EUR-03-2004-E85-BMW-Z4_22i&diagId=33_1148
http://www.realoem.com/bmw/enUS/showparts?id=BT32-EUR-04-2004-E85-BMW-Z4_25i&diagId=33_1148
http://www.realoem.com/bmw/enUS/showparts?id=BT52-EUR-04-2004-E85-BMW-Z4_30i&diagId=33_1148