I use Comedi for voltage output with a PCI card that has 2 analog outputs. I tested the example program ao_waveform from the Comedi library. But I didn't succeed in getting 2 differents outputs for each channel. Either only 1 channel worked or both worked but with the same signal. But both of the channels should give a different voltage series at the same time.

 

Check your addressing.
Add a line that prints out the
contents of the output registers.

Regards
cww