I would like to know if it is possible to connect two speakers via an AUX cable and a Y Adapter to a Raspberry Pi and then use your smartphone (Spotify or Deezer App) to wirelessly control the Raspberry Pi via Bluetooth or Wifi, so that the music is played on both speakers.
Is that possible and if yes what is required for that to work (which Raspberry Pi model would be best and do I need extra equipment for that?)
Any help would be highly appreciated!
This is for sure possible!
Are the speakers active? (e.g. usual computer speakers) If they are, you have to carefully think about powering them. Using GPIO's for that is almost always a bad idea. Consider an additional battery pack in case your project is supposed to be portable.
Other than that, you'd best go with the Pi3, as it already has the hardware you need (BT + Wifi).
All you got to do is boot your Pi to be discoverable by BT devices and forward the audio signal. Look here for a very similiar project. Obviously ignore the BT dongle if going with the Pi3.
If you find an audio hat for the pi which has both RCA and headphone outputs, then you can connect both of your speakers (with amps if necessary) to the Pi. There is a nice selection of sound addons for the pi here : http://elinux.org/index.php?title=RPi_Expansion_Boards#Sound
To control the audio wirelessly, why don't you use some sort of DLNA app on the Pi. For example, if you put a upnp daemon (miniupnpd) on the Pi, it will render audio it gets from the network. You can then have your audio library on the Pi, a separate computer or on your phone acting like a DLNA server. Finally you can control the audio which is being played using a DLNA app (plenty of them to choose from) on your phone.
