Airport express internet radio combination

I have a question i got a amplifier and speaker set in my room and i would like to know if a airport express would allow me to stream music from my nas to my speaker set.

If you add an iTunes server to the mix then the answer is yes. By iTunes server I am referring to running iTunes from either a Mac or PC.

Is it also possible to use tunein radio to play radiostations or spotify?

Yes, but it would require a third-party solution, like Rogue Amoeba's Airfoil, to do so.

I will use my ipad as remote. If it's playing a radiostation for example does my ipad need to stay on?

I assume you mean that the radiostation source is on another device other than the iPad, then no the iPad does not need to stay on.

As you know Spotify, as an Internet audio source, is run via an application on a host device. That application can run on a multitude of devices.

In this case that device is the Spotify streaming "server."

Now, depending on how you want to use the AirPort Express, is what all you would require to stream Spotify to your amplifier/speakers ... and by that I mean, is your goal to use the Express as an AirPlay "speaker" or just to provide a Wi-Fi network that you can stream over?

For AirPlay to work, you would need as a minimum, three components:

1. An iTunes "server." This would be a Mac or PC running iTunes, or an iOS device.
2. A wired or wireless network.
3. An AirPlay "speaker." This could be an AirPort Express, Apple TV, an iOS device, or an AirPlay-ready device provided by another manufacturer.

With AirPlay, you can, of course, stream from iTunes, but as I mentioned earlier, you can use a third-party application to stream from other sources, like Internet radio.

So, for example, to stream Spotify to your amp, the server would be your PC, the wireless network would be provided by the Express, and the Express would also perform as the AirPlay speaker. In turn, you would have the appropriate audio cable connected between the audio port of the Express and the audio input port on your amp.

So basicly if i buy a airport express and connect it to my amplifier that is connected to 2 speakers. I can send music from my ipad to the speakers or even stream radio by using the Tunein radio app?

Correct!

So basicly i don't need to use my pc at all since i have an ipad. Am i right?

Correct again!

By the way i have a synology NAS and it supports itunes server. Does that mean i can play music from my nas on my speakers without using my ipad as streaming server?

Yes.