pm hp tech support.
multi slot boards support multi card but may not support sli or crossfire.
as an example, amd fm2 boards support crossfire but do not support sli, you can use two nvidia cards for work but you cannot sli them, I can fold on two gtx970's but i cannot select sli.
I have two X58 MB neither will SLI Quadro cards just for info, of the card listed above only the FX 3800 has a SLI bridge connector as I remember and being they say you can use two cards it probably works in SLI Multi View not SLI FSAA the latter being what the question is about.
Where do you get it supports Quadro in SLI? I don't see it from the pic you attached but it might say something in the linked info which I did not take time for anything but a quick skim. It does say it will do dual dvi with an adapter, i.e. a "Y" splitter. Neither dual dvi or running dual video cards is the same as SLI.