Thanks Steve for the informative response. AVB looks interesting, although I'm not sure how I feel about the word 'timing' being mentioned in the transfer protocol. If that means that there is no buffer on the receiving end, I'd be a bit concerned, as this means that the final timing consistency of the signal has been coupled with the transfer protocol. And this is precisely what (I would think) should be avoided. If there's still a buffer at the DAC end, and the timing stuff in the protocol helps to better guarantee a more consistent stream of data, then that's all good.
It may be the case that the transfer protocol chosen is independent of using AVB, as it seems that AVB works at a much lower level on the TCP/IP stack (the physical and link layers). So it might make sense to say things like DLNA over AVB.
Although an alternative case for just using straight TCP/IP (and a healthy dose of buffering) is the fact that the internet actually works.