The best way to minimize distortion in a digital board is to control the input. I’ve been using the Aphex 207D on vocal mics for a while now and love the MicLim circuitry that keeps the channel from distorting.

Here I’m running the vocals through a Heil PR35 capsule on a Shure SLX wireless system.  The output of the wireless Rx runs in to the 207D, which converts the signal to digital and runs in to my board through the AES inputs.