Look at Tio. They make small zone player/amps/streaming devices kind of like a Sonos Connect amp, but they go in the single gang hole in the wall where the key pad was. They also make a touch screen version. . Power supply can be down in the rack and feed the amp over the existing cable that used to feed the Abus. Then it uses the speaker wires to feed the speakers. You add as many as you need. One per zone. They are controlled by an app. Etc.

[Link: my.tiohome.com]

Craig