How do I create links from the middle of 1 PDF to another?

I have a collection of FrameMaker books that are delivered as PDfs, all installed locally in the same directory.

I want to add hyperlinks/x-refs that enable users jump from, say, page 10 of docs\Document1.pdf to page 5 of docs\Document2.pdf (i.e. deep linking - making a hyperlink open another PDF at page 1 is easy and  works fine). 

I've been trying out various combinations of x-ref links to to paragraphs and cross-reference markers in the target document, but although the link in the resultant PDF can be clicked, it doesn't go anywhere. The links do

work OK when I have the source and target docs open as FrameMaker docs, but not when saved as PDFs.

Can anybody tell me the correct way of adding x-refs/hyperlinks in Frame 10 so that I can link from the middle of one pdf to the middle of another pdf in the same directory?

I'm runnng:
FM10
Acrobat Distiller + X Pro
Windows 7

Thanks