Reddit mentions of House Band

Take a look at the House Band skill for JRiver Media Server. Requires JRiver, about $50 US (free trial available), but well worth it and highly recommended.

House Band

JRiver

Quick demo

This is definitely not a solution if you are looking to control streaming content through Sonos. But if you are looking to control your local music collection:

https://www.amazon.com/Philosophical-Creations-House-Band/dp/B01ATZM6N4/ref=sr_1_1?s=digital-skills&ie=UTF8&qid=1480192306&sr=1-1&keywords=house+band

I hate the idea of paying for a subscription as well. I can't figure out for the life of me why I can't use Spotify on the Echo for free when I can do so on both my phone and my PC. Pretty lame.
This is not exactly what you've requested, BUT, it's the closest thing I've found to making use of the Echo to control my own music collection. I also haven't set this up yet, but I will be in the next couple of months. From what I understand, if you buy "J. River Media Center" and install the "House Band" Alexa skill (https://www.amazon.com/Philosophical-Creations-House-Band/dp/B01ATZM6N4), you can tell Alexa to play anything from your library as well as control playback over any of your zones. The downside is that I don't think it'll stream over your Echo device. The Echo is used only for control and you need to have a PC running your media player, hooked up to an amp or some other sound system like a Sonos speaker. J. River sells media devices that are essentially power-efficient mini computers with their software installed and a hard drive to store music if you don't like the idea of running a media PC all the time. Good luck!

House Band skill + JRiver Media Center(not free) does this:

https://www.amazon.com/Philosophical-Creations-House-Band/dp/B01ATZM6N4

and eventually some of us hope SONOS will access our personal libraries...