It already sounds excellent. I will research high flow or possibly no cats at all. And maybe like a ram air set up. More air in and more air out.I don't know much about those 944 engines specifically, but I haven't seen many people mod the non-turbo 944 engine variants. Haven't looked much either.
That being said, every Porsche benefits from an aftermarket exhaust. Do that (catback at least) and drive the piss out of it.