I've just received my copy of P&S and am very pleased with it.
One little quibble is that on page 122 the Duke of Bavaria is given as one of the Imperial Electors: He didn't become one until he was given the Upper Palatinate and his Wittelsbach cousin's electoral vote by the Emperor after the start of the war. OTOH the King of Bohemia had a vote but only in Imperial elections, not in the College of Electors in general. Finally, pages 123-4, the throne of Bohemia was elective and Ferdinand was duly elected to it. Peter H. Wilson's book, "The Thirty Years War", is excellent on this stuff.