Hey, I saw that thread, too. I will definitely try it, but will be getting a new cab first. I'm interested in your results, as I'm planning on getting a 2x12, and I noticed you also have 2x12s. I'm probably going to get both 1/2" and 3/4" just to see which gets the best overall result in my particular application.
I also messed my templates up. I had them exactly 12" circles. Little did I know the baffles were actually about 11" diameter. So I need to adjust them all now to 11" in diameter.
Later in the thread, Jay Mitchell said you didn't necessarily have to cut the foam into a donut, thus saving you some labor. The important thing was to keep the hole in the middle, and make sure the foam is big enough so no sound waves would circumvent the outer edges of the foam. The foam could then be placed between the baffle and the grill (not necessarily in the cutout), space allowing.
He also said there are other phenomena going on in multi-speaker cabs, so overall effectiveness might be less than when compared to 1x12 cabs. This was in response to the person using 2x12s.
Keep us updated with the 3/4" results.