You did not say how much time you have given yoursleves for this trip .. I am assuming a month at least.
You will find that for public transport, all roads leave from the Capital.
That is.. in order to get from Pedernales to Jarabacoa, you have to go to Santo Domingo to catch the bus. Now.. there might be a gua gua that might intersect somewhere on the highway but I would not rely on any one to actualy KNOW that.
You will have a lot more fun .. and see a lot more of the country.. if you avoid Caribe Tours pretty much completely except for the big hauls.. like from SD to Dajabon.. and take the smaller buses, the guaguas, which leave from Parque Enriquillo... or Duarte con Paris.. These smaller buses are now pretty much all air conditioned and leave very regularly
For instance, to get to Pedernales, the guagua is easy. If you take the Caribe tours bus, you will have fewer options of leaving times, and then you will have to fit into a crowded guagua for the last few hours from Barahona to Pedernales. Best to just take the guagua all the way. By the time you include the waiting time, the guagua is best (taught to me by several peace corps workers in that area)
There really is no place which is a 9 hour trip.. unless you are trying to get from Dajabon to Punta Cana in one day, I suppose./
Matilda's interactive is interesting but I would not actually COUNT on it.
Jarabacoa .. from Dajabon.. we had to take a bus to La Vega, then a cab cross town to the gua gua.. So I do know that is possible.
There is also the "da me una bola" which is hitch hiking.. which may or may not be dangerous.. depending on where you are and who you are and how your Spanish is and your mind set is.
During these particular times, serious minds would advise against it.
here is a list of the various places which have guaguas..
Lista de Paradas de bus, treny ferry en Repblica Dominicana
the map will then connect to the one Matilda posted.
from this .. you will see that .. for instance, there is no posting for a direct bus from Constanza to Jarabacoa
Horario de Buses de Repblica Dominicana
plus only one bus is posted for leaving .. which I doubt is true.
just as there is only one bus posted for leaving Pedernales..
Bus schedule Dominican Republic
which I KNOW is not true.
But, HEY,, it is ALL about the adventure, right?!??!!!
(note that you should still expect to pay about $1000 pesos a night for a hotel room with a door and a bathroom and cold water and a fan and there are no places to really camp)