A ControlOutProxy is similar to a UGenOutProxy in that it denotes
an output channel of a control UGen. However it refers to a control-proxy
instead of a real control ugen, since the proxies are synthesized into
actual ugens only at the end of a synth graph creation, in order to
clump several controls together. ControlOutProxy instance are typically
returned from the ControlProxyFactory class, that is, using the package
implicits, from calls such as "myControl".kr.