I can't think of a way for you to be able to tell whether or not the NEXT level will be a round or a break. So, the only way to implement this is to have different events for specific times in your tournament. This would tie the event configuration to your blinds schedule, unfortunately, so if you changed your schedule, you would need to possibly adjust your events.
Trigger: A level ends
(state = 2) and (roundNum = 3)
So, use the above when you've got a break after round 3. Create another event for the break that occurs after round 6, for example. And so on. It would be nice to have one generic event that handles playing some audio file after every round in which there will be a break next, but as I said, I can't think of a way to do this.
For the "on break" announcement, I'd simply tie it to a hotkey. Again, it would be nice to have it be automated, but you don't want it to play at some inappropriate time because you had to pause the clock, for example. So, since you'll already have to make sure to START the clock for the break once all hands finish, you would just have to remember to hit some other key to kick off the announcement. I've just added something to the to-do list to allow for firing off a sound or event by pressing a button (<tdbutton> in the layout). That way you could add an on-screen button that plays a sound, for example. I don't *think* you can do this today....