Have no XP with them, but I did use an OMM rack on my Marin mountainbike that had a Marzocchi Bomber suspension fork on it. I used a QR as the lower mount and a linear pull brake bosses as the upper mount (longer hex bolts were provided by OMM (old man mountain).

As far as the fourth thing down the page, it looks OK, so long as you heed their warning about using it on a steel or thick aluminum fork. I think any kind of heavy loads on a thin or CF fork could be disastrous... On a steel fork, you might be able to get a good welder to put braze ons there, or there are also some things called P-clamps that can be mounted on a steel fork too... YMMV, I never went this way and used the QR mount.

Jay