Sonos + Alexa + Dropbox?

No, not possible. Sonos alone cannot play from Dropbox, never mind via Alexa.

Thanks for giving a clear answer; you wouldn't believe how hard that information has been to nail down.
Do you know of a feasible workaround? I guess the base question here is how do I play my personal music library on Sonos?

Your personal library can be share to Sonos from any SMB V1 share on a PC or an NAS drive. See this link:

https://support.sonos.com/s/article/257?language=en_US

Note, at this time you cannot initiate play of local libraries via Alexa. You can start playing from the app, and then use Alexa to pause/resume/skip/rewind, control the volume, and ask what is playing.

So let me summarize what you've said so far. Feel free to correct as needed:
1. Alexa is only helpful for controlling already-playing music.
2. I need to use a laptop (or similar) with Sonos Desktop Controller App, which both connects my library to Sonos and starts/stops playback.

And here are my remaining questions:
1. Do the music files themselves need to be stored in "My Music" on my lappy, or can the app be directed to pull them from Dropbox (assuming Dropbox is downloaded on said lappy)?
2. How does Plex compare with the Sonos controller?

Have a look at the MyPod Alexa skill. https://mypodapp.com/ Works with Sonos, Alexa and Google Drive, and they’ve just enhanced it with their own storage cloud at reasonable rates.

So let me summarize what you've said so far. Feel free to correct as needed:
1. Alexa is only helpful for controlling already-playing music.

If the source is your local music library, yes. If you're using Amazon music or one of the other sources Alexa supports, then no.


2. I need to use a laptop (or similar) with Sonos Desktop Controller App, which both connects my library to Sonos and starts/stops playback.


You don't need a laptop or the desktop controller at all. The Sonos app on a phone/table can setup the connection to the shared drive. That drive can even be something as simple as thumb drive connected to the USB port of a router.


And here are my remaining questions:
1. Do the music files themselves need to be stored in "My Music" on my lappy, or can the app be directed to pull them from Dropbox (assuming Dropbox is downloaded on said lappy)?


It can be any shared drive. Whether there is some sort of dropbox tool that can make your off site music files appear as if they are on a local drive, I don't know. I doubt it.


2. How does Plex compare with the Sonos controller?

I personally don't know much about plex, but Sonos does work with Plex as a source.

You can now roll your own: Amazon makes Music Skill API publicly available. https://venturebeat.com/2018/10/31/music-skill-api-alexa/amp/

Chicks, that's awesome info. Naturally I'm giving you all the credit for the timing of that article. However, I'm too much of a novice in the field to fully appreciate the import. In simple terms, what does that news mean for an end user like me?

Chicks, that's awesome info. Naturally I'm giving you all the credit for the timing of that article. However, I'm too much of a novice in the field to fully appreciate the import. In simple terms, what does that news mean for an end user like me?

Not much, unless you're a skilled developer. There should be a lot more Alexa skills available similar to the MyPod skill mentioned a few posts back, though, as small companies innovate using this API.

OK so let me refocus this thread. You all have been very helpful, but my original question was too narrow, it seems.
I have a fair amount of music ripped from CDs that I'd like to play via a Sonos One. I don't want the music stored on a phone or tablet. How do I do that?