Taking a different approach to my trip. Land in Frankfurt....train to Nuremburg...bus to pilzen. Does the Dbahn ticket to Nuremburg also allow bus transport to Pilzn?
DB ticket to Nuremberg is the ticket to Nuremberg. If you want to go further you need a ticket to that destination, in your case Pilsen (Plzen).
There there is only a handful of buses between Nürnberg and Plzen (the well known DB bus to Praha doesn't stop in Plzen). At most times it's more convenient to take the train with a transfer either in Cheb (northern route) or in Schwandorf (southern route). A through ticket from Frankfurt with a defined intermediate stop at Nürnberg might be cheaper than two separate tickets. Compare that at www.bahn.com first for a direct ticket with an intermediate stop filled in in the appropriate box, secondly for a ticket to Nürnberg and a extra Bayern-Boehmen-ticket which covers you from Nürnberg to Prag. Finally compare the results with the price given by the E-Shop of Czech Rail. Very often they have the best price.