[teeedubb]

Does normal osx steam work ok? You can find the command you need by using 'open' from a terminal, eg

open /Applications/Steam.app/

Note that the osx portion of the script launches programs using a directory.

EDIT: I don't think simply changing the path for steam will be enough - the addon looks for the running process 'steam.sh'. Since steam doesn't run but xbmc restarts you could make a pre-steam script (or rewrite steam-launch.sh to do what you want) to launch steam via wine and wait for it to exit, which will the run the rest of the script and restart xbmc.