Doesn't Cubase have NT problems? I seem to recall that you have to "trick" Cubase into thinking that it isn't NT in order to get it working. Check this with someone who actually got it working.
As for mobos - There aren't too many BX based dual proc mobos on the market. Have a look at the Tyan Tiger 133A Rev. F or Tyan Tiger 100 (S1832). We went over this pretty much a while back so a search here will get you some info as well.
/Ola