and welcome to Armaholic
You are putting the command line wrong, you dont need to have the "Expansion" or "ca" in your
"C:\Program Files (x86)\Bohemia Interactive\ArmA 2\arma2.exe" -noSplash -noFilePatching -showScriptErrors -mod=@ACE;@ACEX;@ACEX_PLA;@ACEX_SM;@CBA
^^that is mine, but im not using steam so its a little different.
Try this one and see if that works:
"D:\Program Files (x86)\Steam\steamapps\common\arma 2 operation arrowhead\arma2oa.exe" -mod=@ACE;@ACEX;@ACEX_RU;@ACEX_SM;@ACEX_USNavy;@CBA
Having a look at this
for steam users can help you launching addons also