Why not group all inputs together electronically, connecting to one board with its own power supply and clock, reclock the data, then convert the signal from all inputs to an optical signal, which is fed via fiber optic cable to the remainder of the DAC circuitry? Of course this is all physically internal to the DAC.
This sees like it would solve a lot of problems with electronic noise, and I wouldn’t think it’d be too difficult or expensive to implement.