I reckon you are over thinking it and getting a bit paranoid, f**k what people think. The cheap aftermarket system may be louder than standard but I wouldn’t have thought by a great deal it may be restricting performance too.
You could get a PMS stealth or if Chris Pickering is doing the piper system get one of them but you still may not be happy with them.
I’m perfectly happy with my K-tec resonated stealth too, it’s one of the quieter aftermarket systems I’ve had on any of my cars. So if someone is getting rid of one of them it’ll be an upgrade to the system you have on it at the moment.