Latencies over a network is an issue regardless of non-synchronized service. In other words "devices that buffer the incoming video" includes device like ... the network itself. Thus, you will have sync issues with anything streaming that doesn't provide a synchronizing service (most if not all do not provide this).
And while there are also latencies involved in doing simultaneous output to the end device (a box that takes for example and HDMI-in and has multiple "mirrored" (and buffered a bit) HDMI-outs), that is likely your best bet for synchronized a/v. Just be aware of the USA's stupid laws with regards to what is a "broadcast" and what is a "public performance"
And on the latter, not saying there is a easy solution, just saying it can be done.