Seems you've done a bit of work with the CM6631A! Are you sure you can derive the required clocks from the 12 MHz one with the CM6631A? Does one require two I2S independent channels to talk to separate ADC and DAC chips? I know The CM6631A can support a DAC, an ADC, and maybe even a CODEC. But how about one ADC and one DAC simultaneously ala XMOS? I'm more interested in something like a high-end D/A A/D solution that may be augmented into a measurebator tool for less than $3000 (hopefully way less). Maybe throw in a low THD+N tone generator(s), distortion magnifiers (or whatevs), switchable attenuators maybe controlled through GPIO of the same uP that is driving the bridge... Something like that. If not possible, not possible. Possible this is a pipe dream. Worst comes to worse we forget about the I2s bridges and awesome sauce DACs and ADCs and just do a Pete Millet upgrade with low THD+N oscillators and distortion magnifiers. Maybe even throw a cheapo separate processor to handle the switches and shit. Possible this is a pipe dream too.