As it turns out the dimensions are exactly the same as the 990 as you suspected. Even the included manual has it listed correctly so they must have a typo on their website. The AVP7/A7200 just fit into the rack.

With the 990 having balanced outputs, DVI switching and far better bass management, it's clearly superior to the Boston AVP7 but I'm not going to complain considering what I paid for it. The Boston looks better IMHO and has a much better remote control.