Peg,
In order to perform the operations you require, you will need to have a single analog output task, and update every analog value for each channel, point-for-point. That is, if you are updating at 1000 samples per second on your sawtooth waveform, you will also need to write 1000 samples per second of DC values for your other channels in LabVIEW. Your program must keep up with the output rate in order to prevent a buffer underrun. An example of this can be found in the LabVIEW Example Finder (Help->Find Examples), called Cont Gen Voltage Wfm-Int Clk-Non Regeneration.vi. Please let me know if you have any questions about this VI or difficulties getting it to work for your application.
Hope this helps,
Ryan Verret
Product Marketing Engineer
Signal Generators
National Instruments