Are you looking to play the same source in both rooms? If so, then as previously suggested, a simple A+B will work, which most receiver have (possibly all). However, if you want to play different sources in each room, then you need a multi-zone receiver, which is much more complicated and expensive.
I used to have a multi-zone A/V receiver in the family room, and used the second zone to power the patio speakers. It was set up so that kids could watch a DVD inside, while the adults listened to music outside. The set up was complicated, and never worked very well. Once I got the SB3, I sent the digital output to the receiver for listening in the family room, and then sent the analog outputs to a simple integrated amp that I purchased used. This set up works much better than the original multi-zone set up.
If you want to keep the costs down, then you could consider a used receiver.
