An 8PSK/QPSK direct conversion tuner IC from STMicroelectronics.
A brochure about the STB6100, including basic specifications, pinout and logical diagram is available here http://www.st.com/stonline/products/literature/bd/10839.pdf.
The full datasheet is not publicly available but some documentation can be found. For example, Comtech Technology has a product brief for a tuner module containing the STB6100 & STB0899, that outlines the basic register and timing info.
Fortunately the information available is sufficient to be able to write a driver for this IC.