Get custom properties from documents

[anykeysolutions]

I can list documents in a folder/list: $files = $list->getRootFolder()->getFiles()->expand('ListItemAllFields');

I can also get all custom properties: $properties = $file->getListItemAllFields();

The problem is, that some properties only content an ID referring to another list. Can I expand these properties and get the actual value from the list somehow by using select or expand in the first action?