but then you have 4 ohm speakers and would either need to wire them in parallel pairs w/ a single zone 8 ohm amp or use a 2 zone, 4 ohm amp. Keeping the amp outside, even in a cabinet, limits your choice in amps if you live in a harsh climate. I would certainly get the Bluetooth separate from the amp since you will have better selection of both amp and Bluetooth, and can upgrade the Bluetooth as technology improves. That said, why not go with something wifi based like a Sonos or Chromecast audio for your source?