What is the difference between the 55SR and 55X? Is it altitude preselect and ILS approach capability? Is the flight director available for 55SR? If there is a flight director and a 55SR installed (and 55SR does not do ILS?,) does the flight director still “fly” the ILS?
I don’t know what the “SR” stands for but in general, the difference from the old 55 and the newer 55X is that the X model has internal GPSS (GPS roll steering) built in.
If perchance you are referring to the SR22 and SRX, it is primairly the SRX is a very stripped version of the SR20, without a lot of the avionics and the wheel pants. I think it was aimed at flight schools to try to get into the initial training market or as an first airplane to feed people into the step up market.