I have an android box that is connected to a couple of speakers. The best I could come up with was using Airtight(airplay clone). It shows up on my Mac for Wireless speakers and I'm able to stream my audio out, but I am also looking for a solution where I can stream audio/spotify from my Android Phone and KindleFire to those speakers as well. I like not having to turn on the TV and that it's available at launch. Ideally, I would like to do it through an Android app but if you all think a Chromecast takes care of it maybe I'll get one.
I use Play Music and have Android devices in my house, so I just use Google Cast. This works for casting to my Google Home devices and CC Audio. You can add a $35 CC Audio to any set of speakers to make them compatible. I also cast to my Shield TV device because Android TV has Google Cast built into it. Any Android TV device should have Google Cast built-in. If you have an "Android box" then that's just regular touchscreen Android. That OS does not act as a receiver for Google Cast.