What I did was lay the foam on top of the visible panel with the standoffs pointing up, then laid the back panel with the speakers carefully on top of that, and locating the standoffs to the holes, carefully pushed it on until it was seated on all 8 standoffs. Then I removed the back speaker panel and carefully eased the foam down over the standoffs until it was laying completely flat on the visible panel (on the inside).
I replaced the rear panel and added the nuts and tightened them down, and when I was done the speaker panel looked pretty good. I don't think I'll need to do anything more. The panels I've completed plus the operator panel (no electronics yet) I set into the built frame so I could see how it looks. I'm pretty impressed with the kit.
(and yea, I've made mistakes. I find documenting them and my solutions helpful to me for future projects.). I'll post today's work tomorrow.
-R