|To be honest, you don't have a lot of choice. iOS and Amazon Fire TV are very different beasts - one it iOS (IPhone, iPad) and the other is Android (as hacked about by Amazon) - so unless you want to write two different apps, your best approach is browser based, or Xamarin - and that means C#.
And do bear in mind that "play on the server" means just that: the client will not be able to see of hear anything unless they are in the same room ... mpg123 is a unix based music player, it won't magically make the sound come out of speakers a thousand miles away.
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