I have struggled for the past few months trying to squeeze a click track out of my ADA8000 outputs, thinking I had not correctly configured my Cubase 5 settings.
I read this article (link now defunct) today, which explains perfectly why the ADA 8000 takes a while (1/2 a second, maybe) to output any audio after you press play. The digital to analogue converters automatically mute audio after a period of digital silence, and take a while to switch back on. This period of silence just happens to be the size of a metronome click, hence, no click track when played by itself.
How to fix this:
You need a constant noise signal to keep the D/A converter from automatically muting; the signal can be inaudibly low, and will still keep the converters from muting in 'digital silence'.
Use a dither plugin on it's lowest setting on each of the ADA8000 output channels.
you can run noise from a test tone generator if your DSP software allows it.