From here I will have to wait at least a few weeks for the LM386 amplifier to come in the mail (I ordered two from different stores, lets see who wins the race...). I am still having thoughts about what to do with the switch, I could use it to enable streaming audio.
I have also considered making it power up from the switch, making the SD card read-only (overlay filesystem) and automatically start streaming whenever the pi boots up.
I haven't looked into what software there is to drive the speaker from my phone, if anyone has a suggestion, drop a note in below. (VLC remote?)
For now, as a bedside speaker this should work fine with quiet audio.
Nothing is glued or stuck down, I also intend on addressing that in the final design as well.
This was the biggest step, getting it all a lot smaller and fitting in the small gap in front of the speaker.
First was to get the strip the parts off the USB sound card, the 3.5mm jacks were the easy part and the USB jack, even though the shield was not soldered in. In the end I got it loose enough to use metal fatigue (wobble the jack back and forth) the the pins broke.
I weighed up whether I should use 5v directly in or use the original nest mini power supply. I could easily go down to the shop, grab the right barrel jack size and go from there, but I do have a few 5v UBECs sitting around for exactly this sort of project.
As these were cheapies off eBay, I wanted to make sire the voltage output from 14V came down to 5V OK. I'm glad I tested the voltage first, the UBEC I grabbed had 12V out, even though it was labelled 5V. Lucky save.