You are talking about connecting a multi-room amp to an AVR, yes?
Zone 2 output on a receiver is often times not volume-controlled by the receiver (and if it is, it will have a volume control that is separate from the main volume control). This is probably ideal if you have a multi-room amp, since you presumably have volume controls for each room. A typical pre-out from a receiver will have be connected to the volume control.
Some receivers will allow for difference concurrent sources being accessed by the respective zones. Primary listening area could be watching TV while zone 2 is listening to a CD (or something). There could also be restrictions on which sources are available for output to the second zone.
I may be missing the mark. Your question was a little vague now that I'm re-reading it. Maybe spell out what you are trying to do and list the equipment you are using.