How to listen to loud music from an android device? I have a music app on my phone. I want to listen to it through nicer speakers than the phone's built-in speakerphone. If I had an iPhone, I'd either use a speaker dock (which both charges the phone and receives music through one port on the bottom of the phone), or I'd use AirPlay. 

Neither of these options seem to be available for Android devices. So, what are the alternatives? Note, this is NOT a request for recommendations of specific products, but a list of available options.
Here are the options I can think of:


Plug a speaker into the headphone jack on the phone. Optionally also plug the phone into a charger.


Will work with any existing equipment.

A bluetooth speaker. 


This recompresses the audio, reducing the sound quality, and inconveniently requires manually going into the settings app to connect to the bluetooth speaker every time you want to use it.

Use a Chromecast to stream to the speakers connected to my TV. 


If you don't have an AV receiver, this means you're probably using the crappy speakers built into the TV. This also only works with apps that support chromecast.

Buy a Sonos. 


Great sound. Works with any audio app. Expensive, proprietary system.

There's a system in some cars that can play music through some android phones' USB port, but I can't find any information on non-car systems that do this, or whether it uses an open or proprietary protocol, or even what it's called. I don't know if it works with all music apps.


If this is it, it seems to me that the state of Android audio is pretty shoddy. I hope I'm missing something. Am I? Is there any new standard on the horizon that might make things better? (If somebody knows of more options, feel free to plagiarize my answer and build on it for your own. I'd rather not accept my own answer! :)