Can I voice control Spotify "Local Files" via Echo to play on a Sonos Gen 1 speaker?

So I'm STILL trying to find a way to use my Amazon Echo and Echo Dots to voice control my music out to my Sonos Play 1 and Play 5 (Gen 1) speakers.

I could use Apple Music back when you could voice control "Favorites". But that functionality was taken away, and I've had no voice control since.

I used Amazon Music for a while, but they don't have all the soundtracks and other music I want to listen to, and now you can't add additional music to Amazon anymore. So I cancelled my subscription and went back to Apple Music.

Apple Music has the biggest library, great quality, and while I'm not a fan of fees, I was prepared to make do. But going without voice control has gotten really annoying. My annual subscription goes till almost year end, but I've set it not to renew.

Since then, I've tried using Synology's skill to control my NAS's music. But besides requiring separate domain names, registration, and port forwarding to allow "Alexa" to navigate from the Cloud to my NAS, it never seemed to find my library and was basically a complete waste. I've given up on this.

Plex seemed to allow me to play my music, but wouldn't play it on a Sonos speaker unless the Sonos had an input (Play 5) and then switching between the input and other options is truly clunky. I tried to enable the "have the speaker switch to the input automatically when music is played", but even then... it seems hokey at best and didn't work as I hoped.

SO... I considered Spotify is supported for voice control, and I wonder if I can use Spotify Local Files to have my NAS music "available" to Spotify, and then voice control those albums, Spotify's "catalog", and whatever else to my Sonos speakers via my echos. If it can, I think I'll need to convert my music from .m4a or whatever "Apple" formats to mp3 that Spotify local files will support. But if it works, it might be worth it.