Trying to increase the HR of the DM11G takes more than just a firmware update. Changes will need to be made to both the software and the hardware.
[EDIT] Ok, I just found out you are not able to set the PLL above 600. It is just not supported. I am sorry for the wrong information earlier.
Its not supported, because there limitation in two places. At first - at web interface, and i was resolve this one. But next check precompilled at cgminer. SCREEN said "pll 610 is too bigXXXXXXXXXXXXXXXXXXXXXx". Please - or give us cgminer source, or remove this check from cgminer. For own risk and with guarranty lost.