1. Buy Zalman heatpipe D
2. Get some screws that will fit into the groove meant for the optional fan.
3. Get whatever fan floats your boat (ex: Nexus 80mm, 92mm, Panaflo 80mm, etc)
4. Slow the fan down with a fan controller if you can get away with it (i.e. the new quiet fan is >= in performance to old heatsink)
5. ... Profit?
Anyway, I did this on my x800xt pe, using the old Zalman heatpipe C with a 92mm Nexus. Undervolted, I'm getting the same performance as my old HSF. It's inaudible in my system.