mwl001,
Get a second amp for zone 2.
Make sure the amp has auto on/off, so a signal arriving at its inputs powers it on, no signal puts it to sleep. I install the Integra ADM2.1 but others do the same at 100 watts. That's 20 watts per channel per zone approximately, which should do you for most listening.
For simplicity, use a Soundolier or Audioplex 6 zone speaker switcher that has amplifier A/B inputs. You can turn any speaker on and off and feed it from the main zone amp (your Sony) or the zone 2 amp. They may have volume controls for each zone as well.
Hope that helps. A simple setup.
=Tom
tomciara@earthlink.net