i have the same deal as you, and i have the apexi evc, your right its not healthy for the engine, when closed, the gas has nowhere to go but back where it came from, but for short times when you need stealth, or to pass certain tests , works a treat.
I havent tested my exhaust at full volume, but when it was 3/4 closed for a pits inspection, i passed by 0.4 db, just make sure your exhaust has no leaks or you will be able to tell there is something extra in there your not meant to have(its illegal, but when the inspector bent down to check, he pretty much just checked to make sure i had a cat)...
But it sounds like your exhaust is louder than mine, so it would just be a temp fix for certain situations.