Sonos / amp needed

I have a Sonos zp100 running a pair of speakers. I want to run a pair of outdoor speakers from the same zp100. Can i just get a cheap 2 channel amp and run the aux output to this amp and run those speakers that way?

I will always be tuned into same station, just want to be able to have seperate volume controls for each. Trrying to avoid buying a second zp100($$$).

Also, is there a cheap amp that i could control volume with iphone?