[beggehorn]

Solved this one (finally!)

After some more troubleshooting (installing different video driver versions and playing with advanced display settings), I discovered that turning off dual display mode for my Matrox P750 restored access to all busses. Further testing revealed that this issue is actually caused when I orient my second display "above" my primary display in Windows display properties (meaning my mouse moves onto the second display when it passes the top border of my primary). I had this set up this way because my second display (Sony Bravia LCD) is on the wall infront of my primary display. When I changed the orientation to place the second monitor to the right of my primary all is good. I can use my dual display setup and my routing assignment list is now *three* columns wide and all 128 busses in my IO setup are available. Excellent!

Hope this helps someone else somewhere down the line