You are using it, by declaring this:
am not using channel6 any where in that xml file.
The consumer that you declared above is built by ConsumerEndpointFactoryBean and this bean has to decide what type of consumer to create (pollable of event driven). It can only make that decision if it knows what type of channel this component is bound too. For example, if CHANNEL6 was a Queue channel, then it would end up to be a Pollable consumer, but if CHANNEL6 is Direct channel, then it would be Event driven.
Without channel present this factory bean can't determine what consumer to build.
As for the auto-startup which is 'true' by default you essentially control when a consumer attaches (subscribes/unsubscribes) itself to a channel to retrieve messages. Look at this as a way of starting or stopping a MessageListener.