I researched this topic for a while, and I came to conclusion that Si-based life is nearly impossible for several reasons.

> Silicon dioxide melting point: 1710 °C

No complex chemistry can survive these temperatures. SiO2 is only soluble in HCl and HF, which are very reactive, so no solubility either.

> Also I don't see why you couldn't have an organism that "breathes" solid material.

All of known biological chemistry relies on some sort of solubility for reagents. I don't think there's any known organism that can get rid of solid waste from the entire volume of the organism.