Hi Matthias,

I don't know how well you know OCD, but I would suggest that you use custom tick boxes to denote formats. Create one for each format (AAC, FLAC, CD and Vinyl). Then - for each record, tick whichever formats apply. Voila - one record in OCD showing 4 different formats.
If you play around a little with the default template (with ocd's own editor, daxedit), you can show all four on your main album page if you want. Or you can just choose to view them by right-clicking a record and looking at its properties. Where you find the information depends on which custom page/tab you have chosen to put them!
Once you have created the custom fields for these formats, you can run searches to find 'all albums on AAC' (for example),and a list will come up in the right-hand pane of OCD. It's very flexible.
If you have any problems doing this, just shout! Hope this helps...