There is no real overall "quality control" if you mean a guy who listens to all releases and kicks them back to the people doing the recording if he thinks it isn't up to snuff. In this sense they are no different than CDs or LPs for that matter - there are good and bad recordings depending on any number of factors.

The basic sound difference between the two formats is nil. Both can sound fantastic with the right material, and of course both are capable of multi channel music reproduction. Sony is the main proponent of SACD, since they developed the format.