Hi Tweakophyte,
First, the numbers for Doable (using the XYZ figures from AVS) are:
L*a*b* = 89.533331, 3.843623, -4.271671
D65 degree Color Temp = 6741.7
These were obtained by using the calculator at
http://www.brucelindbloom.com/index....alculator.html
As for mounting your Doable, how flat is the panel itself? What finished screen size are you after and how large is the Doable sheet? I'm also assuming it's 1/4 inch thick. Sorry if you've given this info before.
As for sealing wood with poly (or anything else)... I wish it were so. Unfortunately all wood finishes do is slow down moisture migration, not stop it. Some are better than others (poly is the best that is available to the home-user). One tip, if you finish a piece of wood, finish BOTH sides. Only finishing one side can actually CAUSE a board to warp due to uneven moisture absorption.
In my experience, plywood thinner than 3/4 inch will curl unless it is prevented from doing so by nails, screws or glue. The exception is Baltic Birch plywood which has many more plys than regular PW and is voidless. It's really nice stuff to work with, but a bit expensive.