If you request ASCII output data, ("run-settings" in the Analysis dialog box) then you can extract stresses in a table format. I have written a matlab script that extracts the max. and min. principal stresses at each node, and calculates the stress range for a series of load sets. I have attached the ptc document that describe the format of these ASCII-files below, and a link to my matlab script. Feel free to use it as you wish. It should be possible to modify it to extract the data you want.
Recall that ASCII output files can be large, make sure you have sufficient local disk space when you run your analysis. It's not a good idea to use a network drive for analysis, at least not for the temporary files. It takes more time for the solver to read / write data over the network.
There is an incosistency though, concerning beam elements. While writing this script I came across a bug in the software. It seems beams, generate a 7x6 matrix with stress results for each h-node. The support documentation suggests that this should always be a 9x6 matrix. I managed to solve this but the problem has now been given SPR-status.
I also recall that there is a technique to convert binary output files into ascii output files, after the analysis has been run. Search the support database for more info on that.