Out of curiousity, why are you attempting to do this with WinRM at the command line instead of building off of the examples in the SDK? They can be configured to use WinRM instead of the DotNetWSman client provided in the library, if you would like. It'd be a lot easier than trying to build the requests directly at the command line with WinRM. In my previous response to your question about how you could load certificates (here: http://software.intel.com/en-us/forums/showthread.php?t=77240 ), I listed some of the other mechanisms you could use to help build the calls. The flow you described has an SDK sample listed at the bottom (it's in the Windows\Intel_AMT\Samples\WS-Management\GeneralInfo directory in the SDK), as a starting point.
I'd recommend looking at that code instead of trying to implement with WinRM at the command line.