Wim,
I believe that NI's PCI-extender is MXI-3, and it connects to a PXI chassis, which is the PCI bus you want with an addition to the backplane for timing. The cards that would go in such a chassis are the PXI cards. This is a very rugged chassis. If you have a catalog, you can see and read about it there; if not, go to www.ni.com, and search for PXI-1000 or MXI-3 (that's the cable).
Mark