KWA does use a different box. Now you can plug in another V2 box and roll but if it's a borked ten cent part that's tough to swallow.
Same goes for Ares, you can put in a whole new mechbox but if you got their stuff for the built in mosfet, quick change spring, etc. and the part you need is $7 if you can get it you're feeling a bit cheated.
Airsoft, where nothing is hurt but feelings.