MrMagoo

Well folks, picked up my new my98 Sti jdm the other day, it's running 307.1bhp proven with equal length headers, fuel dump, mines ecu running 1.1 bar, all looks good on the rollers but I'm looking for advice on the exhaust side of things, loving the sleeper effect with the lack of rumble, but wondering can I run a straight through exhaust on it, as it's too quiet at present? Or will I have to purchase a mappable ecu? The afr on the rollers was spot on, as it stands. What exactly can I do to the car power wise without having to remap?

Suspension and brakes are sorted so just wondering where to go from here?

Any help appreciated.
Mr Magoo