Makes sense! Speaker Central isn't available right now, but will likely be re-released soon. Still, the description in that thread may give you a good idea of whether it will meet your needs. (It handles both speakers and, per a request apparently made just by me that the author was gracious enough to include in an update, notification devices.)
You might be able to re-create something like that using your own logic in a Rule and a virtual notification device (not sure if one exists as a stock driver but it would be easy to create), then sending custom commands to that device, but I haven't tried this so there might be something you can't do that I'm not thinking of...
