I've used the 501HDV with a Canon XH-A1 and I can't tell you how much I hate it. It's not smooth and really doesn't do a good job supporting the weight of my camera (and the XHA1 is lighter than the HVX). If you can afford it, check out the Libec LS-38
I went out on a 2 camera shoot today, and the other person was shooting with a Bogen 503. I was shooting a Vinten Vision 6 & HVX200, but had to use his tripod and Z1U to shoot one shot and it was absolutely horrendous. Very little drag, and when you adjust it for more drag, it doesn't lend itself to smooth movements.
Just my $0.02, but I would not rely on that tripod head for any of my own projects.