I believe the SRA Server is a replacement for the VASA appliance. I think they're trying to wrap it all up under one appliance so that it supports all kind of advanced featuers and what not.
I'm in the process of attempting an SRA upgrade from 2.1 to 4.0 in a testing environment and having issues. Unfortunately, the documenation for this new mess isn't very verbose and there's little community info out there at this point.