Amp connections
Correct, the 2 rca's are for the left in right channel of your zone 2 pre-amp output. Keep in mind, if you are not using 7.1 or presence speakers, your 2500 can power the zone 2 speakers (1 pair @ 8 ohms).
There are a couple different connection methods from the zone 2 amp to the speakers. Most audiosource type 2-channel amps are stable into 4 ohms. Thus, if you have two pairs of 8 ohm speakers, you can directly connect both pairs to the amp. If you want to add more speakers, you will either need additional amps or to implement impedence matching volume controls in each room. This will allow the amp to see an 8 ohm impedence with 2, 4, or 8 pairs of speakers connected. The power is divided, so a 100 Watt/ch amp will deliver 25 Watts to each of 4 speakers. Volume controls or a speaker selector are recommended anyway so that independently control the volume level in each room (loud in one, off in the other, etc.)