ES.EXE is the launcher for the shell (vshell.exe) and the game engine itself (dbsim.exe)
-s: pass through to every launch of vshell and dbsim
-r: pass, whatever is after the "r", to dbsim.exe when it's launched
-a: pass through to every vshell launch
-X: if specifed AND -SPRUNKNOWN has been encountered before (!!), then the first call will not be vshell.exe but dbsim.exe (SPRUNKNOWN is cheat/debug mode, -X is likely something like "go directly to simulator")
-SPRUNKNOWN: Cheat mode. Actually it should not work without the -, but it looks like the decompiler ignores some commands...
-L: pass -l (yeah, lowercase) to dbsim.exe launches
-D: unknown effects. there's dead code in the processor routine... need to investigate this.
SPRUNKNOWN (cheat mode: see http://www.oocities.org/tmn39/cheat/es2.txt for a list of the available commands)
some more, yet undiscovered (have to fully understand the code and how it is called)