I currently own both HFX-9 HD and Juicy Five and I think you will find the Juicys a nice change for DH. They have a nice spongy feel to them and offer alot more modulation then the Hayes traditional 'on/off' bity feel. I run Juicys on my XC bike and I must say, I feel more confidant with the Hayes for some reason for DH...maybe its the fact I run 6" rotors with the Juicys where the Hayes on my other bike have the 8's. Plus, since getting the Hayes, Ive put a bit of effort into getting them up to scratch so I guess compared to the average Hayes user, these probably perform above their usual standard...*shrugs*
Pleanty of people (actually, the majority of people) will tell you otherwise and will almost definatly prefer the Juicys.
Good luck!