hmm im in the same position, bought the car like that, seems to be a full 3" xforce system. Ive got the Apexi ecv u mentioned but controller is not hooked up to the valve. I have been wanting to attach it for a while but havent got round to it. But i will in the next couple weeks as i have already been warned by highway patrol.
Dont know how good the ecv is, doesnt sound like its healthy for the car when valve is closed, so im thinking of getting rid of it and going for a Varex muffler, which is the other option. But also abit cautious on how restricted it is, even when fully open, hopefully not much.
In regard to the db level, its something like 90db when revved to 4000 or 4500rpm, cant remember exactly what the police officer told me. Basically, if u get caught and have to do the db test, u will have to weld a silencer so its not removable to pass or mid muffler i guess. If emissions test, then forget it, stock only option. Thats why its best to not get to this stage otherwise it goes downhill fast.
Anyways thats wat i got to say about the issue