AI Sample Channel and AI Acquire Waveform are functions in the old traditional DAQ driver. The DAQ Assistant uses the newer (and better, imho) DAQmx driver. You should look at the DAQmx low level functions. There are numerous shipping examples. You can also (depending on the version) right click on the Assistant and select Gnerate DAQmx Code or right click on it and select Open Front Panel to view the DAQmx functions that the Assistant is using.
Your other option is to switch to the traditional DAQ driver but then you won't be able to use the DAQ Assistant.