Assume you are correctly spacing the nd5xs and DAC? Don’t physically stack on top of each other, you will be throwing performance out the window.
Remember the NDAC operates with two power supplies when you add an additional PSU.
The internally circuitry is split and decoupled between its internal PSU and the aux PSU.
I suggest keeping the nd5xs2 two small levels or a mid level away from the ndac. I used to run my ndac on top of a Fraim stack … it really does benefit from sensitive placement. As there is no or limited mechanical decoupling