I need to build a multi-directional JQuery parallax page for a client - they basically want it to work in a similar way to this - https://victoriabeckham.landrover.com/INT>
Did you look into librairies like Scrollrama http://johnpolacek.github.com/scrollorama/ or Curtain http://curtain.victorcoulon.fr/?
I know in your question you mention that you already looked into different librairies but depending how they work it's difficult to really suggest how to use proper coordinates.
*edit1
If you didn't see it yet, the auther of scrollorama also did superscrollorama which give a bit more controler over the animation for example animation when an element is pinned.
http://johnpolacek.github.com/superscrollorama/