No doubt there are some improvements which v.584 features. It was what was installed by my AID disc when I used it on my Xecuter 2.6 v1.6 Xbox and I guess for most things it is as good as UnleashX gets.
However there's one feature UnleashX doesn't deliver particularly well in any version and that is the Game Saves Manager. That may not be important for a lot of people here but for me, somebody who is still using it primarily for Xbox gaming, it is.
In short: the v.584 Game Saves Manger is virtually unusable as it won't display individual game saves on any attached memory device. Consequently I've replaced the v.584 with v.572, which is what the same AID disc installs with softmods and, like v.543 I also use, doesn't have the same problem.
But what I was going to say is that if you're having trouble tracking down a source for UnleashX v.584 specifically couldn't AID or another recent alternative installer package be more easily found and used to install the v.584 dash?