Y FWIW customs does include the center options.
Okay, but not sure if the 8500 excludes the center, that's based on the table posted elsewhere, but as I said, not really sure. The 4520 is an excellent unit, I know because I have the AV8801, that's basically a twin on the processing side, except the Marantz has the stupid HDAM modules.
The 4520's amp section is quite powerful too, though not quite as good as the older 4308, you have my spreadsheet, the data are all there. Even when that thing becomes totally obsolete on the processing side, it wouldn't hurt to use it as a power amp.