Harmony is a good option since you can use it to control whatever Amp you want.
Here’s a way to give your existing amplifier Sonos functionality: http://www.sonos.com/en-us/shop/connect.html
If you have a DLNA capable receiver, you should check out this thread: RELEASE Generic Media Renderer (DLNA Speakers). Cheap Sonos Alternative (Update V2)
Good luck!