A liitle extra rail pressure is OK
My 2004. 5 has the EZ and Hot juice stack. The added pressure from the EZ seems to help light off the turbo better and produce a little more power by the seat of my pants meter.
However, I wouldn't add the EZ to any other pressure adder box or pressure increasing downloader. I would be afraid that 2 pressure boxes could damage the rail or injector tips.
I usually leave the EZ in-cab switch on level 1 or 2. I think I drain the rail with the Hot Juice on level 5, (Extreme), and the EZ on the level 3, because it seems to lose power at that setting.
I have run this combo for some time with no ill effects. I have also run the EZ on it's two lower levels with my Smarty separately OK (minus the Juice). Both the Juice and the Smarty can stand a little extra pressure, at least on the Juice and Smarty versions that don't add rail pressure.
I'm not sure about your 2006 Juice. Isn't it able to add rail pressure? If so, I wouldn't think the EZ would be of much benefit.
Just my humble opinion.