well oddly enough the day after I asked myself about Software Crossfire one of the large tech sites from Australia has posted their look at this big improvement for ATI video card users that have X1900 series cards.
Thankfully searching for a Crossfire Master card for my X1900XT is no longer required, I can just grab any make or manufacturing of an X1900GT/XT/XTX and fill the second PCI-e graphics slot and get the boost without the dongle
Tweaktown review