The Meridian 861 will do all you ask. It will handle/synthessize/balance any number of channels from a stereo source and is capable of handling multichannel inputs if you go that way. Furthermore, I see no valid reason for not going all the way to multichannel since, I suspect, that's where you will get the satisfaction you are driving at.
OTOH, you can get wider spread than 45degrees with correctly set-up decent speakers and center fill should not be a problem either.
OTOH, you can get wider spread than 45degrees with correctly set-up decent speakers and center fill should not be a problem either.