8x AGP for Dual Processing Systems?

Paul E. Loeb asks: "I am wondering if there are any solutions out there that will allow the use of an 8x AGP bus with dual processing support. I prefer AMD Athlon MP, but Xeon would be fine as well. I am looking to build a high-end graphics and video editing system, and I don't want to submit to a single Intel or AMD processor. I do however wish to use a Radeon 9700 or GeForce FX, but that would be pretty pointless at a 4x bus. Thank you in advance for all of your advice."