You shouldn't need an active adapter and DP->DVI will work. DP is designed to be backwards compatible with single link DVI. I have an asus board with the pciephy-based DP port and it works fine with both DP directly and DVI via a passive adapter. It sounds to me like your board may have issues if neither the open or closed driver is able to use the DP port. Is it possible that your DP->DVI adapter is bad? Did changing any of those bios options I suggested help?
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890GX/HD4290 dual display question