I was thinking about it and two 8's should give you a similar displacement to a single 12inch which for most people is enough impact. However i still think that for home theater youy really want a response down to 20hz, no matter how you try with an 8 inch it wont happen. Another consideration is that for a vented box you shouldn't really tune to far bellow the stated fs. of the driver. Personally i would try to aim for a tune of roughly 30hz, I will download the parameters of this driver and have a play.
Having thought about it my first sub was an eight and i had a lot of fun designing it and building it. It was tuned to 35hz but it still provided enough bass for movies and music. The only real problem is that in movies you need to watch an 8 because it will KILL itself trying to reproduce 15hz. Would it satisfy me... no but then again if you do not currently have a sub you will notice a significant improvement.
As for the amp i would save and buy a A500 bu behringer which should provide each sub with 170RMS, i really think that plate amp will strugle and clip trying to drive both speakers. Please post some picture.
For music it whould be a good sounding sub, like i said just watch the cones when watching bass heavy music, my 8 goes nuts in U571
well not yay because one day its going to go BANG
