Catalytic Converter

I just bought a 98 XC70 Turbo and was wondering about an aftermarket Catalytic Converter. Can this be done without the Check engine light tripping? I did a little research and found that a Magnaflow would work, but don't know what model or size. Can someone help? The $405 for a direct fit is just a little steep, but I will pay it if that is the ONLY way to go.

Thanks!