Adding a wireless speaker to an existing streaming network

I now stream music from an iMac upstairs (using a Time Capsule) to two different small stereos downstairs, each connected to an Airport Express. So, I can play the same music in three different locations: iMac, stereo A and stereo B. I'd like to add music to another room without the having to deal with speaker wires. Could I use a wireless speaker (such as Bose SoundLink) and add it to the exiting wifi network? In other words, could I get the wireless speaker to show up as a new, 4th location on the Remote app, so that the music playing through the stereos would also stream to the wireless speaker?

Basically I'm trying to get music throughout my house!