That depends on your music provider. If you are a Prime member and only use the included (free) Prime Music, you can only stream to one device at a time. If you try to stream on another device, it'll ask if you want to stop streaming music on the first device. If you have the Amazon Music Unlimited plan (not free), it can stream music to multiple devices at the same time. On the other hand, if your wife listens to Prime Music and you listen to another provider, say Pandora or IHeartRadio, they are from difference sources. And thus there are no restrictions on that. If you have two other Echo devices and stream music from Spotify and TuneIn, you could be playing 4 different music streams from 4 different providers at the same time. Each providers have their own rules on how many devices can play at the same time.