After wrestling with my Sonos system being far from dependable as a voice for my ST, I decided to try use a very cheap Android tablet, Tasker and Sharptools.
Sonos was good, but inconsistent in actually playing the custom phrases or resuming any music it may have disrupted. Custom phrases seem to have their beginning and end lopped off, if you adjust the volume for the message. So, after a year I finally gave up.
I have a mesh of ST devices, with IFTTT acting as a more reliable bridge between my Belkin Wemo devices and ST, SimpleRuleBuilder to build more complex rules for my ST environment, Virtual On/Off tiles to record conditional states, but finally, I have that voice that is reliable.
I bought a cheap Android 5.1 tablet for $50, installed Tasker and Sharptools. Sharptools gives me the add-in to interact with ST within Tasker, so those rules can be complex and driven by or act on ST devices and state.
I let SimpleRulesBuilder make the complex determinations and switch those virtual switches for me, then Tasker reacts to those switch events and decides when it should announce those in one of the available Android TTS voices.
For now this solution works reliably and annoys the hell out of my family, but is a whole lot closer to my HAL9000 home being complete.