Apparently, FIS-based port multiplier support has been in hardware since ICH10 (maybe ICH9), with a linux driver written by the community. But, to date, there has never been windows support from Intel . Most motherboards now have an eSATA port on them and the port still can only be used to add a single drive. For me, adding a card is difficult because I use the Mini-ITX form factor and must use external tuners for my Media Center because my card slot is wasted on a cheap $20 controller card that has drivers for the port-multiplier.
-Valkyrie-MT