In both the TLV320AIC3104 EVM user's guide (http://www.ti.com/lit/ug/slau218/slau218.pdf) and in the register lists in the 3104 data sheet (Table 73), it is suggested that digital microphones can be used with a 3104. However, they reference GPIO that doesn't appear to be there. Do I have to change to a 3106 to use digital microphones?
Yes, the TLV320AIC3106 is the device which supports digital microphones. It looks like the documentation you referenced incorrectly included information about digital microphones for the TLV320AIC3104.
Brandon