Hi,
If I understand you correctly, the solutions is in a typical Visibility / graphics setting.
Linked Revit files by default adopt the view settings of the host file & while all the information travels across (like you noticed) you won’t see it till you specifically set it be visible.
In your building file, go to floor plan you want to see the combination of your building file & the Revit site link + CAD drawing.
Keyboard shortcut: VV or VG for Visibility Graphics, Click Revit Links, & Click on "By host view" for the linked site file.
The easy option, change to "By linked View" & from the drop down select the preferred view you wish to see you link as. Click OK till you back to the drawing area & you should see your link display exactly as it looks in the "original file".
Alternatively select custom, click imported categories, select custom again & notice all fields that were greyed are now available. Just as a fyi, same custom rule applies to all your VG tabs....meaning you can entirely control what you see from a link file & how see it
Hope this helps, if not can create screen shots for you
