Create amd64 DomU in Debain

I am trying to set up an amd64 DomU. I have a cfg file I have been copying to create 686 DomUs (the Dom0 is running an amd64 kernel), but when I use it with the install-arch=amd64 I get an error that it can't find the kernel:

radeon/radeonhd issues with xen domU

I have been trying to export my ATI HD4350 graphics card to a domU. The device is blocked in Dom0 using pciback along with a few other devices and is visible in DomU. All other pci devices work fine. I first tried the radeonhd driver version 1.2.5 (needed to run the newer version from testing