After trying unsuccessfully to improve the audio output of the Raspberry and seeing that I was adding more and more components to the project, I found a very good alternative to the Raspberry Pi, CHIP Pro.

With CHIP Pro I don't need to  buy an external LiPo Charger (like the Powerboost 500) and an external USB audio output, because it has a digital audio output. This combined with a lower price, makes the CHIP Pro an excellent alternative to the Raspberry Pi.

Now I am doing the migration to the new micro processor and a new Enclosure for the prototype.