Currently (2013-07-20) Netflix doesn't support 5.1 surround through a standard PC browser (which uses Silverlight).
Surround sound is supported on devices (Roku, Blu-Ray players, Xbox 360, etc.).
The audio format used is Dolby Digital Plus (DD+), so the AV Receiver must be capable of decoding that format.
It looks like the Windows 8 app does support 5.1 surround sound; see Netflix Features on the Windows 8 App.
The Netflix instant queue is nice to have, but I've been bitten by relying on it too much: when they remove titles (or seasons), they just disappear from your list, so you can't see your previous progress. It would be best to keep track of progress / things to watch in an independent location.
According to http://www.amazon.com/gp/video/ontv/connect it looks like 5.1 surround is supported on PC, but I haven't tried it yet.