It appears that S-A is based on the altitude number, as I can't see an offset relating to the inc/dec buttons. Most other functions (eg. battery switch) are defined as buttons, set via offsets, with in some cases corresponding output offsets to allow reading of the switch state.
In terms of widefs, S-A utilises a server application on the FSX machine, and my (proposed) set up runs all other S-A applications on a seperate low-spec PC. My hardware is connected to the FSX machine and configured in FSUIPC, and I presume the server application handles the communication to the low-spec machine displaying the MCP, Avionics, etc.
From the S-A documentation, it would appear that WideFS could be used as part of the setup, but as my current configuration is only 2 PCs, and hardware is fairly limited at this stage, I do not need that level of complexity.