There are many options. Depends on how "much" are you willing to spend...
You can get multi-zone amplifiers(meaning one amp can accept 2-3 different inputs, and send them, however you wish, to the rest of the house.
Using a speaker selector(like for 4 pairs of speakers) can get tricky. You MUST buy one that does impedance matching. Most "cheap" speaker selector boxes take the ohm load and "halve it" for each pair added in(8 ohm speakers, 2 pairs ran is 4 ohm, 3 pair is 2 ohm, 4 pairs makes an amp killer load of 1 ohm).
So...how do you wish to do this?
Using the 270 to power the 2nd zone, with an impedance matching speaker selector, or running the pre-out to another amp(or amps, with a RCA splitter)...both are "correct" and advisable, if done right.
Also, check your owners manual. Most Onkyo receivers...the "Zone 2 pre-out" does NOT do volume control. It sends out a baseline signal, so the OTHER END has to have volume control.