According to the newest issue of
Megami magazine, The official name for the second season is apparantly going to be "Zero no Tsukaima ~Soutsuki no Kishi~" (ゼロの使い魔～双月の騎士～) (Knight of Twin Moons). This title hints at vol.9 contents since the volume's title was "Soutsuki no Butoukai" (双月の舞踏会). cyan-san from MOON PHASE also suggests that there's a good chance of Tiffania appearing.
I figured vol.8 would be a good cutoff point, since vol.9 and 10 gets Saito into a whole new mess with Henrietta and Tabitha... But oh well, we'll see.