I have xpress pro, and it works okay on my AMD machine, but i've tried upgrading to xpress pro HD, (version 5 and up) and it definatly didn't like it. also, media composer wouldn't even load on my amd machine...
I have been using Avid Xpress Pro DV on my old Athlon 64 3000 and now Avid Xpress Pro HD (v5.7) on my Amd dual core 4600 with zero problems. More of an issue were having to buy a soundblaster because the integrated realtek HD chipset found on many nforce boards is not avid friendly.