The IIR biquad structure requires 5 coefficients. Digital Filter Block supports 128 locations to store coefficients, and so it can directly implement 25 biquad stages (50th order IIR Filter).
It is possible to implement higher order filters by having system software move sets of sample/coefficient data in/out of the DFB Data RAMs in blocks. But the maximum data rate will be reduced due to the overhead of software to service the DFB, and also because the DFB must stall while the System software reads/writes the Data RAMs.
Note: PSoC creator currently does not have support for IIR filter. Please contact Cypress technical support if you need to use DFB for IIR Filter.