I have OpenCockpits MCP and try to make it work using SIOC, FSUIPC and sometimes even hammer.
I'm looking for an idea, what to do, if aircraft model (in my case QWSim Avro RJ) doesn't properly set offsets.
E.g. HDG hold offset is always =1, HDG value is set only when I arm HDGSEL mode (otherwise it seems to be random), and LNAV/VNAV don't change any offset. I managed to programm my MCP's buttons via FSUIPC controls and mouse macro (not ideal, but it works). The problem is with leds. How to get feedback information to light or extinguish leds on buttons?
I'm sure, that you met already those problems in other payware aircrafts. What is your solution?