No reason why the 6xxx series wouldnt work with your motherboard, all X58 boards support Crossfire. I havent heard any rumors about what the next set of nVidia cards might be, they arent even done filling up the 4xx line up so a new generation of cards is a ways away for them.
A single 480 is fine for most resolutions, if you want max performance grab a single 5970 now and then grab two of the flagship 6xxx series cards once they are released a little later in the year.
Who ever is telling you that is a moron. All P55 and X58 boards are crossfire compatible, their chipset natively supports crossfire and since there is no liscensing fee all the boards do too. There seems to be this strange convoluted theory that people cook up about AMD working better with ATI but this isnt the case, a 5970 will perform just as well on an X58 system as it would on an 890FX board, but X58 board means you have an i7 and an OC'ed i7 removes any relevant CPU bottleneck from the picture, so if we are going to be saying an ATI card works better with anything it works better with an OC'ed i7.
Thanks for the help. I think I will wait till November for the ATI 6 series cards and get 2 of them. Unless Nvidia has something up their sleave Im not aware of. I tried Nvidias 3D technology and I wasn't impressed. I did hear that the 6 series may have 3D tech this round though. Id rather have better frame rates and resolution with the ATI cards.