If I connect the PCM5122 to the PAM8406 AFTER the output load RC filter, then there is noise introduced into the PAM8406 (exterior noise that can't be filtered).
What does work is connecting the output of the PCM5122 directly to the PAM8406 through a ferrite bead, into a 1uF DC blocking capacitor and into the 18k input resistor on the PAM8406.
My question is: Are there any potential issues that would arise from not using a load resistor?
The PCM5122 output filter differs from the TI recommendations because the extra output load thwarts the noise present on the output (it's inherent to the system that the unit is being plugged into).
Output gain on the PCM5122 is 0dB right now. I may actually tune that further down to prevent clipping via the device gain registers.
The amplifier is set to 24dB gain as the system it's expected to drive an in-car telephone system (and must therefore be quite audible). The PAM works well in its current configuration, FWIW.