Carsten,
You do have some flexibility as to how you export various information such as channel names, comments, etc. to the *.DAT file, and it sounds like you've found that already. Once your data is in a *.DAT file, you can choose to load some or all of the channels and some or all of the values in these channels with the "File>>Paste from file" pull-down menu option in DIAdem-DATA. This enables you to do selective loading of data sets stored as *.DAT files. I don't know if this is what you're looking for, but it's a real useful feature that at the least you will be glad to know about at some point.
It sounds like you really need DIAdem 9 in order to conveniently browse the Citadel 5 data base natively in DIA
dem. For the next few months, at least, you could use the DIAdem 9 Beta, which times out in February. If you go to the DIAdem Beta site and sign up/register, I can push your profile live, and you can work with DIAdem 9 for a few months. That would at least solve your short-term problem.
Brad