Good question. mt-daapd sends them in the order they are specified in the playlist.
What the client does with them is it’s business. iTunes sorts them, but I don’t belive Roku does. So iTunes puts them in the order it feels is most appropriate, while the soundbridge displays them in the order that they come from mt-daapd.
Bottom line is that mt-daapd can “suggest” and order, but the client is ultimately responsible for determining order.