Gotcha,thanks. 
Unless you replace the internal wiring harness with that of a 580, you're only going to be able to swap Color Classic and 520/550/575 boards. Like I said before, the logic board connector is reversed, starting with the 580.Interesting discussion thanks for all the info. My main goal though is to find a motherboard other than the 575 board that I can put into the 575 chasis. Because the 575 motherboard is going in the Color Classic. I asked about the 6500 motherboard, because I can purchase it online for cheap.