Our client can generate his XLIFF's fairly flexible. But we would need a way to show comments or remarks that are stored in the XLIFF in Trados.

A custom XML filetype is not a good option, as we need the get both the source and the target text already aligned in the XLIFF. 

Supplying that with a TMX is not an option either, as there would be lots similar segments with different matches.

I've tried this:

 <unit id="1">
  <notes>
   <note id="n1" appliesTo="target">Please check the 
     translation for 'namespace'. On also can use 'espace de nom',
     but I think most technical manuals use the English term.
    </note>
   </notes> 
  <segment>
    <source>Namespace</source>
    <target>Whatever the translation</target>
   </segment>
 </unit>

But those notes are ignored. Any ideas? Is there another way?