Hi Michael,
I understand that you are using the RTLSDR toolbox in MATLAB to record IQ data from a RTL-SDR device, but the output data is saved as a matrix with rows representing samples per frame and columns representing frames. However, you would like to get a single stream of data similar to what you obtained with SDR# or the Ettus E310 SDR.
To achieve a single stream of IQ data, you can simply concatenate the columns of the matrix into a single column vector using the 'reshape' function.