It won't be back in stock for 3 more weeks and they will fill backorders first. I'm assuming the amp will be centered in the back panel. I checked out the dado blades and didn't want to dish out the money, but the biscuit joiner worked great and it only took me about 5 minutes.
I'm going to go ahead and cut the hole for the amp. It looks like it has a pretty good overhang, unlike the speaker. I'll have the speaker on Thursday...