1. Within a DAQmx Task, all channels shares a single sampling rate, so different channels cannot sample with different sampling rate.
2. If the 2 DAQmx Task using channels from same DAQ module, LabVIEW Error must pop up. It is because DAQmx task will locked the DAQ module and prevent others to access. You can config the DAQ channels in LabVIEW with DAQmx vi. Same configuration can be achieved in LabVIEW & MAX.
3. The output of DAQ assistant is dynamic data, but not 2D array. You can convert it by VI "Convert from dynamic data", choose option "2D array of scalars, rows are channels", then you will get same result as with DAQmx Read