An 8" driver will 12 mm of exursion would only get to within a 1/4 of the metal at full excursion. I don't know of an 8" with the 18mm of excursion needed to hit the hole. Besides, the piston area of an average 8" driver is about 6.5 inches. If you wanted to be extra safe, go with a 1" adapter. There are very few drivers in existence with a 25mm xmax, and none with an 8" diameter, unless you can find an 8" TC Sounds driver from the Sunfire 8" sub which is highly unlikely.
