It helps to post your vi.
Any way, If your vi works for one channel, then it should work for multiple channels.
You have to us the proper syntax for multiple channels
For single channel, you are using (assuming Daqmx, )physical channel syntax
Dev1/ai0 for channel 0
for multiple channels, use
Dev1/ai0:1 for channels 0, 1
Dev1/ai0:2 for channels 0,1,2
Dev1/ai0,Dev1/ai2 for channels 0 and 2
etc..
and make sure that the daqmx read has the option
Analog 1D wfm
NChan NSamp
is selected.
Then the wave form data will be an array, with undex 0 being for the first channel in the list, and index 1 for the second channel in the list and so on