I did go with plan X. I soldered a header on the DAC, and the OSPi, and just used jumpers between the pertinent pins.
I did end up with a “ground loop” hum through my 12 volt app. I did not have that with just the pi and DAC. It only happened when the OSPi 24VAC power was plugged in. I solved it by connecting a ground between the DAC and OSPi (pin 9), then also, from the OSPi (pin 39) to the ground of the AMP.
Works great, now 😎!