According to the window announcement of a bookstore, the second season of "Shinkyoku Soukai Polyphonica" was announced. It will be aired from the spring 2009. The official website is counting down for a surprising news, probably the official announcement of the new season. The number of Bourai is increasing as the countdown advances.

Source: the picture of the window announcement
Source: Official website

Edited on Nov 12th======================
The countdown finished and the official website was finally open. The title of the second season is "Shinkyoku Soukai Polyphonica crimson S".

Edited on Dec 6th=========================
According to NewType magazine, the production staff are as follows:

Director: Suzuki Toshimasa ("Heroic Age")
Series organizer: Kanemaki Kenichi ("Pani Poni Dash!")
Script writer: Kawasaki Hiroyuki ("Tsubasa Chronicle")
Character designer: Obara Mitsuru ("Peach Girl")
Production company: Diomedia (former name: Studio Barcelona)

Source: MOONPHASE