Ok, here are the photos of the two solenoid boxes and the parkway box. The parkway box is the one I think has a Febco type double check assembly.
http://s1159.photobucket.com/albums/p632/texasf/
Have you found your solution yet? I found the same issues as your posts just last week, that multiple zones are turned on at the same time with low pressure. I am living in Plano, north of Dallas. I am trying to figure out the problem and fix. It'd be great if you can share your findings/solutions. Thanks.