sdurani (and Prefect): No, I can't set center to None. I am stuck with Small if left and right are Small and Small or Large if left and right are Large. I even had a hard time disabling the surround speakers (I'm starting out with a 2.1 system -- my old strictly audio preamp died so I purchased my 990 sooner than I otherwise would have), though I succeeded by futzing around.

Navigating the speaker configuration menu is like a maze: the options for some speakers depend on the options set for others, and it's not clear what affects what.