Point of interest: I pulled up a Revit Systems Plus 2 file in Revit Building 9.1 and exported a DWF. That file imported into FMDesktop without a whimper. I don't know if I'll be able to do that after the 30-day evaluation period, though, or if any important information might not transfer from Systems Plus 2 to Building 9.1.
There is an easy, no-cost way to get data from Revit Systems Plus 2 to FMDesktop 7.
1. Find a copy of Revit Building 9.1 (not 9.0). If you don't have the distribution disks, download a copy from http://usa.autodesk.com/adsk/servlet/item?siteID=123112&id=9262404
I picked Revit Building 9.1 for Autodesk AutoCAD Revit Series—Building 9.1.
2. Install as Standalone Trial or Demo. The Trial give you a fully functional copy for 30 days. After 30 days, it reverts to Demo mode for legal, indefinite use.
3. Both modes allow you to retrieve files saved in Revit Building Systems 2 and print, plot, and export to DWF. Just follow the normal procedure to export DWFs from Building 9.1 to FMDesktop.