How is preventing you from updating your software until you agree to a privacy policy a backdoor?

That's a good point, there must be a way to block access from these devices to the Sonos mothership. I have seen zero software improvement in the few years I owned my Sonos set, so I can't say that I would miss much.

Not as many as you'd think.

That's the ballpark price of a standard Sonos 5.1 home theatre set.

I think around 6

The sonos subwoofer alone is about half of that price.

Does Logitech Media Server integrate with all these doodads: http://www.sonos.com/en-us/streaming-music ?

Great advice. I've had squeezeboxes since the SB1 in 2003, and recently got a Hifiberry amp running Squeezelite. It's as minimal as it gets -- power brick, RPi + amp in a custom case, and speakers. The class D amp is surprisingly pleasant.

I second this. I've been using various squeezebox devices (and software players) for years, for both listening to my own music collection as well as streaming (spotify mostly). The squeezebox server (i.e the core software that various clients can connect to) has been open-sourced, and is still actively developed/updated. There are also open-source software clients readily available.

What's the latency like? I've got some Qualcomm Allcast gear that seems to do sync properly with no perceptible delay, but it's the only one I've heard that does it properly.