Technically, you need a power amp.
But, depending on how many channels of your amp you're using in your main area, you might be able to utilize two unused power amps in your receiver for this. RTFM or perhaps others more familiar with your exact unit might chime in here.
But, if you DO need to get an amp for the second zone, you may find a two channel integrated amp (or even a two channel receiver) might afford you a little more control over the signal in that second zone (volume, tone, etc...)