Predecessor in the "MX world": MX644.
MS440 is only available with the 21MTC interface, but in two variants (-D and -C), which differ in the design of the higher function outputs (FA3 to FA6 as open collector or logic level), although the variants can be converted into one another by means of CV programming (for self-correction of incorrect orders). 21MTC was the most widespread interface for a while (around the years 2000 to 2010), but has lost over time compared to PluX, as it actually offers fewer function outputs and there is a certain "chaos of standards"; This is related to the fact that it was originally designed for electronically commutated motors ("C-Sinus"), which have now disappeared from the model railroad world.
There are NO wired versions of the MS440; these would be superfluous as they would have the same properties, dimensions, etc. as the MS450, but with fewer outputs.
"MS-Sound" with 3W fully digital sound amplifier for 8 ohms or 4 ohms (or two 8 ohms in parallel) loudspeakers; exactly the same as MS450.
"Stay-alive": Direct connection for external energy storage - 16V electrolytic capacitors or 15V supercap (without upper capacity limit); technically completely the same as MS450, but energy storage connection on wires (due to the interface standard).