As you have found software is key for any sort of streaming or whole house audio. I used to have Sonos, sold it and never looked back.
I use a Node to do all my streaming either from local files or internet. I use an external DAC and separates like any regular mid to high end stereo. I am not a fan of the Sonos amps as they are way overpriced but are convenient.
It is easy to use any amp you want from the Node and another option here (different software) is the Wiim Amp which can prob drive the speakers as well or better than the Sonos amp and is a streamer too. I have no other bluesound products as many brands can easily be used with the Node.
FWIW, you can run your existing Sonos speakers with JRiver software. The Sonos speakers are renderers or endpoints, I forget and JRiver sees them. Since JRiver sees them you can play thru them. Gapless playback is not reliable tho. JRiver software is pretty good and there is an iOS version (App Store) which I used to use to control the speakers.
The bluesound software I like and is generally found to be easy to use. I have not used the software the Wiim user do tho. And as you know Sonos has blown two major software releases in the last few years.